The Merit Systems Protection Board (Board) sustained the removal of Alton Webster, a civilian postal clerk at an Army installation, finding an adequate basis therefor because of five incidents of “serious” misconduct involving insubordination, failure to follow his supervisor’s instructions, open disrespect to his supervisor and to a military officer, and creating a disturbance. Webster v. Department of Army, Docket No. AT07528910316 (MSPB May 11, 1989). The initial decision became final on June 15, 1989, because Webster failed to file for review by the full Board; he then filed a timely appeal, pro se, under 5 U.S.C. § 7703(b)(1) (1988), over which we have jurisdiction under 28 U.S.C. § 1295(a)(9) (1988). Because the Administrative Judge (AJ) adequately considered all relevant Douglas factors as to alleged disproportionate penalty, properly applied correct legal standards and burdens in deciding the issue of alleged retaliation, and based his conclusions on findings supported by substantial evidence, we affirm.
BACKGROUND
Webster was employed by the Department of the Army as a civilian mail clerk charged to assist military mail clerks and units at Fort Bragg with regulatory compliance and training. Webster, slip op. at 15. He was removed, effective December 30, 1988, based on eleven specifications, including incidents of insubordination, creating a disturbance resulting in an adverse effect on morale and maintenance of proper discipline, disrespect towards his supervisor (all second offenses), discourtesy, willful violation of rules and regulations, and willful use of a government vehicle for other than official business. Id. at 1-2. His removal was recommended by his supervisor, Mr. Willie L. McCain, and ordered by Ms. Judith Bickford, who apparently was three levels above petitioner in the postal chain of command.
Webster appealed his removal to the Board. After a full evidentiary hearing on March 28, 1989, the AJ dismissed six specifications but sustained the following five, finding each supported by a preponderance of the evidence:
1. On September 13, 1988, Webster failed to report to his supervisor prior to turning in his government vehicle, contrary to his supervisor’s express instructions. The other employees received the very same specific instruction, i.e., to report daily to the supervisor at the postal branch, in person or by phone, prior to 1615 hours and before turning in their vehicles. Statements of Annie G. McLaughlin, Edgar Chapman and Willie L. McCain, compiled in Webster, Docket No. AT07528910316 (Tab 4K-4) [hereinafter compiled in Board Record]. It is undisputed that all but Webster complied. Webster, slip op. at 6-7. Despite repeated reminders from McCain, on this occasion Webster plainly did not obey. Notice of Proposed Removal, by Judith Bickford, Chief, Operations/Systems Integration Division (Oct. 19, 1988) [hereinafter Notice of Proposed Removal (Oct. 19, 1988) ], compiled in Board Record (Tab 4J).
Webster argued as justification or excuse that he disagreed with the need to report to his supervisor, McCain, because, he said, “the policy did not make sense.” Webster, slip op. at 7 (AJ Finding of Fact); Notice of Proposed Removal (Oct. 19, 1988) (Bickford quoting Webster’s statement.). The AJ did not accept Webster’s personal opinion about the lack of value of the instruction as a valid excuse. Webster’s brief to us also argued that McCain had agreed to exempt him from compliance. He cited no testimony, however, in support of this contention. The AJ found the specification proven.
*6822.On September 15, two days later, Webster failed to assemble and remain in front of the post office during a fire drill as instructed and as all the other postal employees did; instead, immediately upon departing the building, he left the area. Both not assembling out front and departing the area were contrary to supervisor McCain’s explicit instructions. The AJ found McCain “instructed all employees to assemble on the lawn in front of the [building].” Webster, slip op. at 7. McCain stated he instructed all personnel to “fall out on the grass in front of the Postal Branch.... ” Disposition Form, by Willie L. McCain, Chief, Postal/Distribution Branch (Sept. 21, 1988), compiled in Board Record (Tab 4K-4). Other employees stated they were instructed to “go outside to the field located between the Post Office and [the road]” and to “assemble outside on the grass.” Statements of Warren P. Basnight and Peggy E. Worcester (Sept. 16 & 23, 1988, respectively), compiled in Board Record (Tab 4K-4). It is undisputed that Webster neither assembled nor remained with the other employees. When Webster failed to appear, McCain went looking for him. The AJ found Webster “left the area to get some ice cream.” Webster, slip op. at 7. Upon Webster’s return, McCain told him he had not received permission to leave. The record reflects that McCain asked Webster why he did not stay for the fire drill. Webster stated he had vacated the building and that was all that was required. McCain reminded Webster he had instructed everyone “to assemble outside on the grass” and explained that he “was in charge of the assembly.” Disposition Form, by Willie L. McCain, Chief, Postal/Distribution Branch (Sept. 21, 1988) compiled in Board Record (Tab 4K-4). Webster conceded he responded to McCain’s statement that as supervisor he was in charge, saying, “In charge of what?” Webster, slip op. at 7.
Webster also testified, and now argues before us, that he was either on union time or break time during the fire drill assembly. As the AJ noted, “[Webster’s] testimony on this issue is internally inconsistent.” Id. The AJ also found it unsupported on both points. Id. The AJ therefore concluded, “I have rejected the appellant’s testimony on this issue.” Id. Rejecting Webster’s other excuses, the AJ sustained a charge of insubordination and also one of disrespectful conduct.
3. On October 17, about one month later, Webster failed to follow a specific instruction from McCain to use a rubber stamp to mark mail to be forwarded and did not do so on three letters. Id. at 10. Before the AJ, Webster testified he was not told to use the stamp; however, the AJ found that Webster was so instructed but failed to follow the instruction. Id. at 10-11. The AJ sustained the specification for failure to follow the supervisor’s stamping instruction.
The AJ also found Webster was disrespectful to McCain. Id. at 11. Webster argued with McCain, stating that this procedure was not required on another Army base. Id. Procedures at other Army bases were not viewed as controlling with regard to procedures required at Fort Bragg. Nor was it found sufficient that a Department of Defense mail manual did not require the procedure followed at Fort Bragg. The AJ found Webster stated that he knew more about mail procedures than his supervisor. Because of that statement, the AJ found Webster “intentionally challenged his supervisor’s authority.” Id.
4. About two weeks later, on November 1, 1988, Webster loudly interrupted a conversation inside the postal facility about complying with postal procedures that Lt. Michelle Perna and Sgt. Reese were conducting with Mr. Chapman, another civilian postal employee, with a “childish tirade.” According to the AJ’s findings, Webster yelled at Lt. Perna, used crude language, and “embarrassed and humiliated” the military personnel. Id. Lt. Perna, a platoon leader, reported the incident herself. At the hearing, according to the AJ, she testified “that the appellant was rude and disrespectful to her_” Id. (emphasis added). In his testimony, Webster conceded he intervened in Lt. Perna’s meeting, which did not concern him, and referred to someone as a “jack asshole.” Id. at 12. As the AJ *683noted, her account of the incident was corroborated by Mr. Chapman. Id.
The AJ sustained charges that Webster created a disturbance and was discourteous to the military personnel. Id.
5. On November 8, when McCain questioned whether Webster had sent certain mail on distribution, Webster responded, “Are you crazy?” Id. Webster contended he was provoked by his supervisor, but the AJ noted Webster “offered no evidence to support this assertion.” Id. The AJ sustained a charge that Webster had been disrespectful to his supervisor. Id.
In addition to the five sustained specifications for misconduct in 1988, Webster had a prior disciplinary record for four charges of misconduct in 1987, for which he was reprimanded. In 1987 McCain had proposed a five-day suspension because Webster failed to heed his request that Webster stop dropping books on the floor, but instead responded that he “didn’t ‘give a fuck.’ ” Id. at 16. The record reflects that this incident occurred in the presence of Webster’s co-workers. In responding to McCain’s proposal to suspend Webster, Bickford, the deciding official, wrote, “Although there is no excuse for [Webster’s August 24, 1987] behavior, Mr. Webster’s supervisor is partially responsible for the turmoil in this branch.” Disposition Form, by Judith Bickford, Acting Chief (Nov. 17, 1987) (Record of Prior Disciplinary Action), compiled in Board Record (Tab L). Consequently, Bickford determined Webster would receive a written reprimand rather than a suspension. He was reprimanded by letter of February 1, 1988, for “insubordination, disrespect toward his supervisor, creating a disturbance, and use of abusive and offensive language” in August, 1987. Webster, slip op. at 16.
Webster had replied to the proposed 1987 suspension, alleging “that the action was in reprisal for a complaint he took to the union.” Id. Apparently, his claim was rejected by Bickford. The AJ found there was no reason to discount this prior misconduct. Webster was specifically warned in the letter of reprimand that “future incidents of this nature will not be tolerated and will be the basis for more severe disciplinary action.” Notice of Decision-Reprimand, by Judith Bickford, Acting Chief (Dec. 3, 1987), compiled in Board Record (Tab L).
The AJ found that Webster’s 1988 offenses directly “impacted” the efficiency of the service. Webster, slip op. at 14. Specifically, the AJ found Webster had “openly defied his supervisor and created confusion and tension in the work environment.” Id. at 15 (emphasis added). Such findings, together with his finding that appellant showed no remorse, id. at 17, provided the stated basis for the AJ’s upholding an adverse action against Webster.
As to the appropriateness of the removal penalty, the AJ expressly weighed the Douglas factors relevant to this case. Id. at 15-17. The AJ noted that the removal penalty was consistent with the agency’s table of penalties. The AJ stated: “The agency cannot tolerate disrespectful conduct to a supervisor, the open refusal to follow supervisory directives and discourteous conduct to military personnel.” Id. at 16 (emphasis added). Webster’s argument that the agency had “overexaggerated his conduct” in selecting the removal penalty was specifically considered. See id. The AJ disagreed with Webster’s view, finding the misconduct “serious.” Id. Noting also Webster’s prior record for three of the same offenses, the AJ concluded: “I find that the removal penalty is not excessive, disproportionate to the sustained offense [sic] or arbitrary, capricious, or unreasonable.” Id. at 17.
In front of the AJ, Webster raised two affirmative defenses. Webster alleged race or color discrimination because the removing official was white and he is black. The AJ, however, rejected the defense because “the appellant did not present any evidence or argument” in support. Id. at 12 (emphasis added).1
*684As before, Webster also defended against the charges on the ground of retaliation for union-related activity as well as for contacting a U.S. Postal Inspector and a U.S. Senator to complain about McCain. Noting that the supervisors were aware of Webster’s protected activity, the AJ found that the “adverse action under review could, under the circumstances, have been retaliation.” Id. at 13. Finding that “the sustained offenses are serious,” id. at 16, and “[t]he four incidents involving Mr. McCain all involve active misconduct on appellant’s part,” id. at 14, the AJ found that, despite the agency’s high retaliatory motive, the discipline actually resulted from “the objective facts.” Id. Webster offered no evidence of disparate treatment for other Army postal employees who engaged in similar conduct. The AJ rejected the defense of retaliation. Id.
OPINION
I. The Five Specifications Sustained
After reviewing the record, the briefs, and the AJ’s opinion, we hold that none of . the findings is arbitrary or capricious or unsupported by substantial evidence and none of the conclusions is an abuse of discretion, was reached without required procedures or is contrary to law. 5 U.S.C. § 7703(c) (1988).
All five specifications sustained were supported by substantial evidence on the record before us. In addition to resting heavily on credibility determinations concerning the various agency witnesses and Webster, the AJ’s findings are in many cases undisputed by Webster, who admits to the conduct alleged but offers excuses. We hold they were properly rejected as legally insufficient. Beyond the facts set forth in our Background section, we explicitly address only the two sustained specifications which the dissent believes were not supported by substantial evidence.
Webster was found insubordinate because he violated a specific, repeated instruction to report to his supervisor, daily, before turning in his vehicle. It is undisputed that on September 13, 1988, Webster did not report as instructed.
We think that in such a military/postal employment setting, the efficiency of the service requires that an immediate supervisor’s lawful instructions must be followed by clerks like Webster, even if they think the instructions are foolish, and even if they are correct. It was Webster’s duty to follow the reporting instruction. Therefore, whether or not McCain’s instruction was wise, Webster’s noncompliance cannot be excused.
The dissent questions why the AJ “discredited”' Webster’s excuse for defying the “policy” of reporting in, particularly since, despite his noncompliance, Webster did not incur overtime costs, the sole purpose of the policy. The record reflects, however, that what is referred to as a “policy” was not only of long standing, but was actually an explicit instruction which McCain had repeatedly and personally counselled Webster to follow. Notice of • Proposed Removal, compiled in Board Record (Tab J). Far from disbelieving Webster, the AJ, by necessary implication,2 determined his excuse was legally insufficient. We cannot disagree. While the dissent also faults the AJ for “defective” analysis on this issue, we think that the AJ’s failure to explain specifically why he was unpersuaded by Webster’s excuse, when it was legally irrelevant, cannot constitute reversible error. Webster cites no authority requiring insubordination to be flagrant or continual before discipline may be imposed. We have said that insubordination “is a willful and intentional refusal to obey an authorized order of a superior officer which the officer is entitled to have obeyed.” Phillips v. General Servs. Ad*685min., 878 F.2d 370, 373 (Fed.Cir.1989). There was substantial evidence that Webster violated a lawful instruction, without lawful excuse.
The dissent next expresses concern that this one infraction is de minimis, merely a procedural violation. Although, by itself, this single incident may not be “serious” or, alone, sufficient to support removal, it must be, as it was, considered by the AJ along with the other four sustained incidents in determining that Webster’s combined misconduct was “serious.” Furthermore, no authority is offered to support the proposition that violations of instructions cannot support disciplinary action if they are merely procedural.
Likewise, we hold there is substantial evidence to support the finding Webster was insubordinate regarding the fire drill instruction. The AJ found that McCain instructed everyone “to assemble on the lawn,” Webster, slip op. at 7, and the record reflects McCain shouted, “Fire, fire, fall out on the grass in front of the Postal Branch....” Disposition Form, by Willie L. McCain, Chief, Postal/Distribution Branch (Sept. 21, 1988), compiled in Board Record (Tab 4K-4) (emphasis added). As everyone knows who is familiar with terminology commonly used on an Army base, even by civilian employees, “fall out” means assemble and remain assembled until expressly dismissed or otherwise instructed.
McCain’s own testimony was by no means the only evidence of the specific content of his fire drill instruction. The record also contains statements by employees that he instructed them to assemble and remain at a designated place outside. See Statements of Warren P. Basnight and Peggy E. Worcester (Sept. 16 & 23, 1988, respectively), compiled in Board Record (Tab 4K-4). McCain asserts he saw Webster leave the building with the other personnel but then he could not find Webster in the designated assembly area. Disposition Form, by Willie L. McCain, Chief, Postal/Distribution Branch (Sept. 21, 1988), compiled in Board Record (Tab 4K-4). The reason, according to the AJ’s finding, was that Webster left the area to get ice cream. Webster, slip op. at 7. Webster admits departing and making the statement to McCain on his return that the AJ found disrespectful.
As to whether McCain instructed Webster to assemble for the fire drill, the AJ found that McCain “instructed all employees to assemble on the lawn in front of the branch.” Id. (emphasis added). Employees are quoted in the record as agreeing that McCain instructed them to “assemble outside on the grass” and that McCain reported he told everyone to “fall out on the grass,” as reflected in the Disposition Form he made less than a week after the fire drill incident. The record reflects that Webster “was present at his desk” when the fire drill was called. Disposition Form, by Willie L. McCain, Chief, Postal/Distribution Branch (Sept. 1, 1988), compiled in Board Record (Tab 4K-4). Thus, Webster was present and it cannot reasonably be disputed that he heard the instruction to assemble. In addition, the specific content of his fire drill instruction was testified to by McCain and the AJ believed that testimony. Accordingly, there was substantial evidence to support the AJ’s finding that McCain “instructed all employees to assemble on the lawn in front of the [postal] branch.” Webster, slip op. at 7. Thus, there is substantial evidence of record to support the AJ’s sustaining charges for Webster’s insubordination and disrespect to his supervisor.
II. Penalty
Petitioner argues that the penalty of removal is excessive for the five specifications, of the original eleven brought, that were sustained by the AJ. Our review of penalty, however, is highly deferential. It is well-established that selecting the penalty for employee misconduct is left to the agency’s discretion. Parker v. United States Postal Serv., 819 F.2d 1113, 1116 (Fed.Cir.1987) (“[DJeference is given to the agency’s judgment ... unless the penalty is so harsh and unconscionably disproportionate to the offense that it amounts to an abuse of discretion.”) (internal quotations *686omitted) (emphasis added); DeWitt v. Department of Navy, 747 F.2d 1442, 1445 (Fed.Cir.1984), cert. denied, 470 U.S. 1054, 105 S.Ct. 1759, 84 L.Ed.2d 822 (1985) (“This court will not disturb the agency’s choice unless the severity of its action appears totally unwarranted in light of the relevant factors.”) (emphasis added). While, as the AJ acknowledged, the penalty must be reasonable in light of the sustained charges, our court has effectively defined reasonable in this context to mean merely that the agency’s choice of penalty not be “grossly disproportionate to the of-fense_” Miguel v. Department of Army, 727 F.2d 1081, 1083 (Fed.Cir.1984). Whether this court would have chosen a different penalty is irrelevant. See Hunt v. Department of Health and Human Servs., 758 F.2d 608, 611 (Fed.Cir.1985). Here, the AJ found the agency had not properly considered the Douglas factors and therefore independently considered and discussed them himself. Webster, slip op. at 16.
A. Compliance with Douglas
The AJ specifically analyzed the removal penalty in light of each of the four factors of 12 enumerated in Douglas v. Veterans Administration, 5 M.S.P.R. 280 (1981), applicable to the facts of this case. The AJ determined that the removal action was “appropriate and reasonable under the circumstances.” Webster, slip op. at 15. We think a fair reading of the AJ’s lengthy opinion as a whole demonstrates “that the presiding official identified, balanced and then considered the relevant Douglas factors in determining that the sustained charge[s] warranted the penalty imposed.” Kline v. Department of Transp., 808 F.2d 43, 46 (Fed.Cir.1986). Indeed, the penalty discussion itself is probably sufficient on its face. See Webster, slip op. at 14-17.
Petitioner argues, however, that he was not given an adequate Douglas factor review. Apparently, petitioner objects that the other factors listed in Douglas were not discussed by the AJ. But the AJ need not consider every one of the 12 Douglas factors “mechanistically by [a] preordained formula.” Douglas, 5 M.S.P.R. at 306. In his Douglas review in the penalty section of his opinion, the AJ explicitly addressed the nature and seriousness of the five charges he sustained. The AJ also expressly considered petitioner’s past disciplinary and performance records, and the deleterious effect of his course of misconduct on his ability to perform his job. Webster, slip op. at 15. The AJ found that the five sustained charges of misconduct have a “direct nexus to the efficiency of the service” and that Webster’s duties included assisting military mail clerks and units with regulatory compliance and training. Id. Further, the AJ noted Webster had a short tenure, a prior disciplinary record with the Army including three of the same violations, and failed to express any remorse. See id. at 15-17. The AJ’s conclusion that the agency did not abuse its discretion in selecting removal cannot be overturned on the basis of the AJ’s opinion and its discussion of the Douglas factors.
B. Provocation as Mitigation
One of the Douglas factors requires consideration of “mitigating circumstances surrounding the offense[s] such as ... personality problems ... or provocation on the part of others involved in the matter[s].” 5 M.S.P.R. at 305. Moreover, unless all “significant mitigating circumstance[s]” are considered, the adverse action cannot be sustained. Van Fossen v. Department of Hous. and Urban Dev., 748 F.2d 1579, 1581 (Fed.Cir.1984) (emphasis added).
The dissent criticizes the Board for its “failure to consider an important factor relating to mitigation” regarding Webster’s removal, namely “the animus of Supervisor McCain towards Webster.” Far from failing to consider it, the AJ discussed it explicitly. Further, he found “the appellant’s supercilious and boastful demeanor generated some personal animus with his supervisors.” Webster, slip op. at 14 (emphasis added). Thus the AJ did address “the animus of Supervisor McCain towards Webster,” apparently finding it attributable more to Webster than McCain. The AJ also found that Webster “actively sought *687to confront [McCain] at every opportunity.” Regardless of its genesis, however, the AJ, by necessary implication, found that the animosity did not cause the removal.3 Id.
But even assuming that personal animus against Webster was caused solely by McCain, and that it was a factor in McCain’s recommendation of removal, Bickford, the removing official, was herself neutral and aware of McCain’s prior attitude about Webster. Indeed, the year before she reduced the penalty recommended by McCain specifically because of “turmoil in the branch.” That she did not do so again in 1988 may suggest that she did not find turmoil or animus was a significant factor then. In any event, there is simply no record basis to question her neutrality. Webster has offered no direct evidence of animus on her part. The AJ made no finding of such animus. We cannot conclude he was compelled to make such an inference, either. See Frampton v. Department of Interior, 880 F.2d 1314, 1317 (Fed. Cir.1989) (Employee failed to prove his supervisor, the proposing official, was motivated by “personal animus” and “neither showed nor even alleged that [the removing official] had a retaliatory motive.”). Moreover, it appears she was two levels above McCain. Any animus between McCain and Webster, whether generated by Webster or by McCain, or by both, is therefore eliminated as a significant motivating factor in Bickford’s decision to remove Webster. Her impartiality is apparent from her knowledge of McCain’s attitude toward Webster, her reduction of the prior penalty, and her lack of personal involvement in either the tension between McCain and Webster or Webster’s protected activity. It is not insignificant that Webster’s complaint to the Postal Inspector and the Senator concerned McCain, but not Bickford. Indeed, the AJ effectively found Ms. Bickford was neutral when he referred to “objective facts” supporting the adverse action. Id.
The AJ clearly found that the penalty was reasonable, i.e., not grossly disproportionate, based on the gravity of the sustained offenses, Webster’s prior disciplinary record, his short tenure, and his lack of remorse. The AJ discussed each of these items individually. Again, Bickford’s neutrality is important because she actually made the decision to remove. The AJ concluded that animus was not a significant factor either as to taking an adverse action or as to selecting the penalty of removal. A fair reading of the AJ’s opinion as a whole demonstrates that the AJ did not fail to consider animus as a mitigating factor in determining the lawfulness of the penalty, or to consider it adequately.
C. Opinion Read as a Whole
The most serious criticism that can be directed against the AJ’s penalty discussion, id. at 14-17, is that it does not repeat all the findings stated earlier that are also relevant to penalty. For example, in the section analyzing the sustainability of each of the specifications, the AJ stated that Webster “embarrassed and humiliated” military personnel, Lt. Perna. Id. at 11. This could have been, but was not, explicitly repeated in the penalty discussion as relating to the Douglas factor concerning how the offenses affected his “supervisors’ confidence in [Webster’s] ability to perform [his] duties,” which included training military mail clerks. 5 M.S.P.R. at 305. Similarly, Webster was found insubordinate: He ignored instructions to assemble and remain in front of the post office during a fire drill, a time when even more than usual employees must be relied upon to follow instructions. See Disposition Form, by Willie L. McCain, Chief, Postal/Distribution Branch (Sept. 1, 1988), compiled in Board Record (Tab 4K-4). This incident, too, could have been discussed again in relation to the Douglas factor regarding Webster’s “dependability.” 5 M.S.P.R. at 305. Likewise, Webster’s other repeated incidents of disrespect and insubordination could have been discussed again in the context of the Douglas factor regarding *688“whether the offense[s were] intentional ... or frequently repeated.” Id.
Each incident, however, was adequately detailed in the context of describing the charges sustained; they need not be repeated in the penalty discussion. In the final analysis, challenges to the organization of the AJ’s opinion are simply not grounds for reversing the Board’s decision.
D. Gravity of the Misconduct
The question remains whether the AJ’s fact findings relevant to the penalty of removal, as opposed to lesser potential alternatives, were unsupported by substantial evidence. The AJ found that “the sustained offenses are serious.” Webster, slip op. at 16. We cannot overturn that finding on this record. The dissent minimizes the seriousness of the sustained charges noting that the AJ must assess the underlying conduct, not just its labels. We conclude from our review of the AJ’s opinion as a whole that he did indeed weigh the underlying conduct and did so adequately. Moreover, we conclude that, like the AJ, we must consider the conduct in context. The AJ properly noted that the U.S. Army “cannot tolerate disrespectful conduct to a supervisor, the open refusal to follow supervisory directives and discourteous conduct to military personnel.” Id. (emphasis added). The AJ thus supported his conclusion that in light of Webster’s conduct, the Army’s decision to remove him was justified for the efficiency of the service, based on the five specifications sustained. Id. at 14; see Bassett v. Department of Navy, 34 M.S.P.R. 66, 69 (1987) (“The disobedience of proper orders by an employee is done at the risk of being insubordinate and may be sufficient cause for removal” — three incidents in eight months); see also Roberson v. Veterans Admin., 27 M.S.P.R. 489, 494 (1985) (abusive language and disrespectful behavior can constitute just cause for removal).
In this regard, the AJ’s finding that petitioner “was discourteous and he created a disturbance” in his confrontation with Lt. Michelle Perna, Webster, slip op. at 12, is particularly important. Although we need not and do not so conclude, the Perna incident alone might have put Webster’s removal within the discretion of the agency because his position was at a postal facility on a military base and his duties brought him into regular contact with military personnel, both commissioned and enlisted, including mail clerks in military units. As the AJ noted, “disrespectful behavior is not acceptable conduct, not conductive [sic] to a stable working atmosphere and may constitute just cause for removal.” Id. at 14 (citations omitted). That principle may apply with even greater force in a military setting, as here, for Webster must operate both at the postal facility and in military units and work directly with not only civilians, but also with soldiers. Unfortunately, the record shows he was equally disrespectful to his own supervisor and the military personnel.
Moreover, the record reveals that, like several of his other incidents of discourtesy, Webster’s tirade to Lt. Perna was overheard by other military personnel and other postal workers. The corrosive effect of such a public spectacle on military discipline and postal employee morale cannot be overlooked. The AJ noted that “Lt. Perna is a Platoon Leader” and “was embarrassed and humiliated by the appellant’s conduct” which included rudely interrupting, yelling, and referring to someone as a “jack asshole.” Id. at 11-12. Indeed, Lt. Perna’s report of the incident states that Webster yelled directly at her and refused to lower his voice, despite her request. Statement of Lt. Perna, compiled in Board Record (Tab 4G). The AJ also noted that “Lt. Perna reported the incident herself.” Id. at 14. We conclude the AJ did consider and reasonably assess the underlying conduct. In finding it sufficiently serious to warrant removal, the AJ concluded the Army did not abuse its discretion. We agree. We simply cannot say removal is totally unwarranted or unconscionably or grossly disproportionate to the sustained offenses.
III. Reprisal
Petitioner contests his removal as taken in reprisal for his activities as a *689new union shop steward and for letters written to a U.S. Senator and a U.S. Postal Inspector complaining about McCain. In part, his contentions mirror those rejected in his prior disciplinary proceeding when he claimed he was being sanctioned for grieving to the union. The AJ demonstrated he correctly understood the applicable legal test when he stated that:
To establish reprisal as an affirmative defense, [Webster] must meet the test for reprisal as restated by the Federal Circuit in Warren v. Department of the Army, 804 F.2d 654, 656-58 (Fed.Cir.1986). The four elements of this test are: (1) The employee engaged in a protected activity; (2) the accused official knew of the protected activity; (3) the adverse action under review could, under the circumstances, have been retaliation; and (4) there was genuine nexus between the retaliation and the adverse action.
Webster, slip op. at 3.
Applying the four part Warren test to the facts, the AJ found that Webster was engaged in protected activities; that his supervisors were aware of the activities; and that the adverse action under review “could, under the circumstances, have been retaliation.” Id. at 13 (emphasis added). Those findings, establishing the first three elements of the Warren test, are supported by substantial evidence. For the affirmative defense of reprisal to be established, however, the AJ must also make a fourth finding: that there is a genuine nexus between the retaliatory motive4 and the adverse action. But no such finding was made here. Nor was one compelled by this record, although the dissent concludes otherwise.
Warren specifically states that the petitioner “has the burden” of establishing the four elements of retaliation. 804 F.2d at 656, quoting Hagmeyer, 757 F.2d at 1284; see Stromfeld v. Department of Justice, 21 M.S.P.R. 428, 431 (1984) (employee has the burden of establishing a prima facie case of reprisal); see also Mortensen v. Department of Army, 27 M.S.P.R. 433, 437 (1985); Kennedy v. Department of Army, 22 M.S.P.R. 190, 193 (1984). Thus, the AJ properly placed the burden on Webster to “meet the test for reprisal.” Webster, slip op. at 3. Webster must carry his burden of demonstrating, prima facie, that retaliatory motive was a significant causal factor for the adverse action. Cf. National Labor Relations Bd. v. Transportation Mgmt. Corp., 462 U.S. 393, 401, 103 S.Ct. 2469, 2474, 76 L.Ed.2d 667 (1983); Mount Healthy School Dist. v. Doyle, 429 U.S. 274, 287, 97 S.Ct. 568, 576, 50 L.Ed.2d 471 (1977); see Stromfeld, 21 M.S.P.R. at 431 (burden shifts from the petitioner once all elements of reprisal are established, including “causal connection between the protected activity and the adverse action,” i.e., nexus).
The burden of demonstrating a “nexus” between “the retaliation and petitioner’s removal,” Warren, 804 F.2d at 656, ultimately involves establishing a causal connection between the protected activity and the adverse action, as the Board correctly phrased it in Stromfeld, 21 M.S.P.R. at 431.
Nor is the burden too onerous. Petitioner is not required to produce direct evidence of the deciding official’s intent, but only evidence from which the AJ can properly infer that the retaliatory motive caused the adverse action. Warren, 804 F.2d at 657, quoting In re Frazier, 1 M.S.P.R. 163, 193 (1979). Because direct evidence, such as an explicit admission, rarely is available, the Board has accurately noted, “in almost all situations [the causal connection] must be inferred from circumstantial evidence.” McClellan v. United States Postal Serv., 19 M.S.P.R. 237, 239 (1984); see Frazier, 1 M.S.P.R. at 194. If, for example, Webster had offered evidence of other employees at his postal facility who engaged in comparable conduct but *690received more lenient sanctions, the AJ could have found nexus was established. See Stromfeld, 21 M.S.P.R. at 432 (Employee attempted to show that other employees “committed more serious acts of misconduct than he and were either not disciplined or less severely disciplined.”). Webster would be likely to know of any disparate disciplinary action taken, or indeed not taken, against similarly situated fellow workers who engaged in comparable conduct.
On the record before us, however, petitioner offered no such evidence. The AJ did not find that Webster’s protected activities caused the adverse action and we cannot say this record, as a matter of law, requires such an inference of nexus.
The AJ did find that “the intensity of the agency’s retaliatory motive was high.” Webster, slip op. at 14. He then weighed the high intensity retaliatory motive against the gravity of the misconduct. Although he found that retaliatory motive “could” have been a factor, he did not find that the retaliatory motive was a factor in Webster’s removal. Retaliatory motive does not, ipso facto require a finding of causation. The dissent glosses over this important distinction between “could have been” (element 3) and “was” (element 4), but it is dispositive of this appeal.
The AJ found that of the five of eleven specifications sustained, four involved McCain and one involved Lt. Perna, that Lt. Perna reported the incident herself, and that the four incidents involving McCain all included active misconduct on Webster’s part. The AJ then found “that an imaginary supervisory [sic] who was unaware of [Webster’s] protected conduct would conclude from the objective facts that an adverse action was warranted.” Accordingly, the AJ concluded that the affirmative defense of reprisal failed. Id.
The AJ’s finding about an “imaginary supervisor” followed, nearly verbatim, the test we stated in Warren: An adverse action may be sustained if the AJ finds “in effect, that an imaginary supervisor who knew nothing of the [protected activity] would have been led by the objective facts to find [the employee’s misconduct warranted removal].” 804 F.2d at 659. Furthermore, unless petitioner establishes all four elements of reprisal, prima facie, Warren simply requires nothing of the agency. If reprisal has been proven, prima facie, Warren requires nothing more of the agency than that it present proof on the basis of which the AJ could find that an “imaginary supervisor” would have taken an adverse action, anyway.5 Where a prima facie case of reprisal has been established, the fact finder should evaluate any rebuttal evidence offered in light of the questions so elaborately set forth in the dissent. If the AJ does so find, the agency has rebutted the prima facie case of retaliation.
The AJ implicitly found Webster’s removal was not caused by his protected activity and explicitly found it was caused by his conduct, based on the evidence submitted, including the repetition and gravity of the 1988 conduct as well as his prior disciplinary record. That the AJ could have inferred retaliation (nexus) does not mean, as a matter of law he had to. The AJ’s findings relating to possible retaliation depended heavily on his assessing credibility and weighing conflicting evidence, particularly concerning the gravity *691and excusability of Webster’s conduct. Petitioner simply has not shown how the AJ’s ultimate finding against him as to reprisal, or any of the necessary underlying findings, is unsupported by substantial evidence. Accordingly, we hold that petitioner failed to establish prima facie retaliation and therefore without need of any rebuttal evidence by the agency, on this record his defense of retaliation must fail. That the AJ nevertheless applied the “imaginary supervisor” test does not constitute reversible error, especially where, as here, the finding is intertwined with whether petitioner has established nexus. For example, if the AJ had found Webster’s conduct was less serious or partly excusable, the inference might be drawn that retaliation had been established prima facie. In any event, it would make little sense to direct the AJ not to consider previously submitted agency evidence relevant to retaliation unless he has already found a prima facie case, including nexus.
In sum, this appeal must be resolved under Warren. Properly construed, the Warren test is not met by demonstrating that a retaliatory motive “could have” been the cause of the adverse action. That merely meets element three of the affirmative defense of reprisal. The third element can be met, for example, by showing that the removing official might well have resented the protected activity as where it reflected poorly on him. Conversely, if the adverse action preceded the protected activity, one cannot conclude the former “could have been” the cause of the latter. Once the third element of the reprisal defense is met, however, the petitioner must still persuade the AJ of nexus, i.e., causation in fact. Here the AJ was not so persuaded. We cannot reverse because on this record any such inference, even if permissible, certainly was not mandatory.
CONCLUSION
The sustained specifications are supported by substantial evidence. The findings fully support the conclusion that petitioner’s pattern of disruptive misconduct undermined military discipline and postal employee morale and impaired the efficiency of Army postal operations. His open insubordination, open refusal to follow instructions, and public disrespect to his supervisor and to military personnel were particularly harmful. Therefore an adverse action was lawful. Petitioner has failed to demonstrate that, despite his repeated misconduct in 1988, his prior disciplinary record for three of the same offenses in 1987, and his lack of remorse, his removal was “grossly disproportionate” to the five offenses sustained and thus an abuse of the agency’s discretion. Nor has he shown his removal was retaliatory because petitioner did not carry his burden to show nexus: that his protected activity created animus leading to retaliatory motive that actually caused his removal. The AJ’s decision must therefore be
AFFIRMED.
. Before us, Webster does not assert race or color discrimination, which would divest this court of subject matter jurisdiction, provided the discrimination allegation was nonfrivolous. *684See Hill v. Department of the Air Force, 796 F.2d 1469, 1471 (Fed.Cir.1986) (“minimal prima facie case” of discrimination required).
. It is well established that an appellate court may infer findings necessary to explicit findings oí a prior tribunal. See, e.g., Bott v. Four Star Corp., 807 F.2d 1567, 1576 (Fed.Cir.1986); see generally 5A J.W. Moore & J.D. Lucas, Federal Practice ¶ 52.06[2], at 151-52 (2d ed.1989).
. The dissent speculates that McCain’s animus against Webster, deemed by Bickford to be present in 1987, continued through 1988. The AJ did not make such an inference. Nor on this record was the AJ, as a matter of law, required to draw such an inference.
. Although Warren, uses the word "retaliation," 804 F.2d at 656, quoting Hagmeyer v. United States, 757 F.2d 1281, 1284 (Fed.Cir.1985), the majority makes clear that this term must be understood as referring to retaliatory motive since "retaliation” is the conclusion that follows only if all four elements of the test are met and since, if understood literally, it would make element (3) moot element (4). See Warren, 804 F.2d at 656-57, 658.
. As this case and Warren both illustrate, even where nexus was not established by petitioner, the AJ, exceeding any requirement, often will take the precaution to determine "whether there are independent grounds for initiating an action against an employee." 804 F.2d at 657. By doing so, he provides an alternative ground of decision that would control if a reviewing court overruled the finding on the failure to establish a prima facie case of retaliation. See Rogers v. Department of Defense Schools, 814 F.2d 1549, 1555 (Fed.Cir.1987) (Some evidence of retaliation is insufficient if there is "substantial evidence that [petitioner’s] removal was based on legitimate employment considerations.”). It simply is not legal error for the agency to submit, and the AJ to consider, evidence of the agency’s legitimate employment considerations to aid in the determination of whether petitioner has established nexus. It simply cannot be a prerequisite to consideration of such proof that first the burden must shift, particularly where, as here, that evidence was also relevant to proving the misconduct charged and thus is submitted in the agency’s case in chief.