After a jury deadlocked at his first trial, Paul Coles was retried on charges of *487armed robbery1 and possession of a firearm during the commission of a crime of violence (PFCV)2 relating to the robbery at gunpoint of Redoduane Abderrafe. The jury at his second trial found Coles guilty on both counts, and he now appeals. Coles’ primary contention is that the trial judge committed reversible error by restricting Coles’ cross-examination of a prosecution witness. We disagree and affirm.
I.
THE EVIDENCE
At Coles’ trial, the prosecution presented evidence which, if credited, established that late at night on July 30, 1997, two men robbed Abderrafe at gunpoint as he walked down a street in Georgetown shortly after he completed his work shift as a waiter at a local restaurant. After the robbers took the tips that Abderrafe had earned, one of the men ordered him to “[g]o — don’t turn your back. Just go straight.” The two men then fled on foot. Abderrafe continued to walk as instructed, but almost immediately he encountered Officer Joseph Thomas of the Metropolitan Police Department. Abderrafe told Officer Thomas that he had been robbed, and he described one of the two robbers to the officer as “not too tall, not too short” and as wearing “tan military pants and [a] white shirt.” Based on this information, Officer Thomas broadcast a lookout over the police radio.
Several police officers working in the Georgetown area monitored the broadcast. After pursuing several other leads, they spotted and began to chase a man who discarded a “speed loader,” a wallet, a black stocking cap, and some personal documents shortly before he was apprehended. The man turned out to be Paul Coles, the appellant in this case. Officers also recovered a handgun which Coles had allegedly dropped earlier in the chase.
On July 22, 1998, a grand jury returned a nine-count indictment against Coles, charging him with involvement in three separate robberies, one of which was the robbery of Mr. Abderrafe. Coles’ first trial was held before Judge Rhonda Reid Winston from October 5 to October 21, 1999. The jury found Coles guilty of unlawful possession of ammunition in connection with the Abderrafe robbery, but deadlocked on the armed robbery and PFCV charges.3 We affirmed the conviction for ammunition possession in Coles v. United States, No. 99-CV-1017, Memorandum Opinion and Judgment (D.C. March 6, 2001).
From October 11 to October 13, 2000, a second jury trial was held before Judge Natalia M. Combs Greene with respect to the charges of armed robbery and PFCV. The jury at the second trial found Coles guilty on both counts. This appeal followed.
II.
THE ATTEMPTED IMPEACHMENT FOR BIAS
The only issue raised by Coles on appeal which merits plenary consideration is whether the trial judge erred by limiting the cross-examination of Kurt Goodwine, a witness for the prosecution.4 We discern *488no legal error or abuse of discretion. In our view, the limitation of which Coles complains pertained to a matter of very little, if any, probative value, and its exclusion was justified by its potential for distracting the jury from the issue at hand. At the very least, the trial judge could reasonably so conclude.
A. Background.
During the prosecution’s ease-in-chief, Goodwine testified that he had sold defendant Coles a Smith and Wesson handgun, as well as ammunition and a speed loader, when the two men were employed by the Department of the Navy approximately five years before the trial. Goodwine identified Government’s Exhibit No. 2, by its serial number, as the weapon that he. had sold to Coles. Exhibit No. 2 was the handgun that Coles had allegedly dropped during the officers’ pursuit of him. On cross-examination, Goodwine acknowledged that he had no documentation of the sale of the handgun to Coles, and he was unable to recall either the precise date of the transaction or the exact amount paid to him by Coles.
Coles’ attorney then attempted to cross-examine Goodwine regarding an employment discrimination complaint that Coles had allegedly filed in January 1999 against Goodwine’s superior at the Navy Department. The judge inquired as to the relevance of the question, and counsel proffered that the proposed fine of inquiry would demonstrate that Goodwine was biased against Coles. Counsel explained that Goodwine had been called as a management witness by the Department of the Navy in an administrative hearing on Coles’ complaint. Subsequently, in January 2000, Goodwine had stated in an affidavit that Coles “had a deleterious effect on morale of the section because none of us could understand his motivation and we could all see where this was heading.”5
The judge indicated that she did not see how the discrimination complaint provided Goodwine with a motive to fabricate evidence falsely implicating Coles in an armed robbery. She pointed out that if the proposed questioning was permitted, the prosecutor would have the right to *489bring out the witness’ position. Coles’ attorney acknowledged that this was so: “Oh, no question.” The judge then explained that she did not propose to try what she regarded as a collateral matter (namely, the rights and wrongs of Good-wine’s criticism of Coles in connection with the discrimination case):
I’m not going to try that [discrimination] case. I think, you know, bias is always relevant, that is true, but given when this affidavit was given, the circumstances under which it was given, an administrative action where this witness was just called as a witness, that he was not alleged to have been one of the discriminators or that he took any action against your client, I don’t see how that is probative of bias in terms of — I’m not going to turn this into some discrimination trial.
Coles’ attorney then argued that Good-wine’s motive was to “curry favor with his boss.” The judge disagreed and declined to permit the proposed cross-examination.
B. Legal Analysis.
A criminal defendant’s right to cross-examine prosecution witnesses is protected by the Confrontation Clause of the Sixth Amendment. Davis v. Alaska, 415 U.S. 308, 315, 94 S.Ct. 1105, 39 L.Ed.2d 347 (1974); Lawrence v. United States, 482 A.2d 374, 376 (D.C.1984). That right, however, is not unlimited. Reed v. United States, 452 A.2d 1173, 1176 (D.C.1982), cert. denied, 464 U.S. 839, 104 S.Ct. 132, 78 L.Ed.2d 127 (1983). “[D]espite the Sixth Amendment, the trial court has broad discretion to impose reasonable limits on cross-examination based on concerns about, among other things, harassment, prejudice, confusion of the issues, the witness’ safety, or interrogation that is repetitive or only marginally relevant.” Grayton v. United States, 745 A.2d 274, 280-81 (D.C.2000) (citations and internal quotation marks omitted). “A proposed line of questioning may, and should, be disallowed if the trial court concludes that its probative value is substantially outweighed by the danger of unfair prejudice,” id. at 281; see also Mercer v. United States, 724 A.2d 1176, 1184 (D.C.1999), or if the inquiry may divert the attention of the jury from the issue at hand. The trial judge has “wide latitude insofar as the Confrontation Clause is concerned to impose reasonable limits on cross examination,” Delaware v. Van Arsdall, 475 U.S. 673, 679, 106 S.Ct. 1431, 89 L.Ed.2d 674 (1986), for she has “the responsibility for seeing that the sideshow does not take over the circus.” Ed-waRD W. CleaRY, McCoRmick on Evidence § 40, at 89 (3d ed.1984).
In the present case, the proposed cross-examination was designed to impeach Goodwine for bias:
Bias is a term used in the “common law of evidence” to describe the relationship between a party and a witness which might lead the witness to slant, unconsciously or otherwise, his testimony in favor of or against a party. Bias may be induced by a witness’ like, dislike, or fear of a party, or by the witness’ self-interest.
United States v. Abel, 469 U.S. 45, 52, 105 S.Ct. 465, 83 L.Ed.2d 450 (1984). Bias is “always relevant,” Hollingsworth v. United States, 531 A.2d 973, 979 (D.C.1987), and “[t]he Supreme Court has established that the refusal to allow any questioning about facts indicative of bias from which the jury could reasonably draw adverse inferences ... is an error of constitutional dimension, violating the defendant’s rights secured by the Confrontation Clause.” Ford v. United States, 549 A.2d 1124, 1126 (D.C.1988) (emphasis in original) (citing Van Arsdall, supra, 475 U.S. at 678-79, 106 S.Ct. 1431). Here, the judge allowed *490no cross-examination regarding Good-wine’s purported bias, which was alleged to have stemmed from Coles’ discrimination complaint. But
the party posing the question must proffer to the court some facts which support a genuine belief that the witness is biased in the manner asserted, that there is a specific personal bias on the part of the witness, and that the proposed questions are probative of bias.
Barnes v. United States, 614 A.2d 902, 905 (D.C.1992) (emphasis added) (quoting Porter v. United States, 561 A.2d 994, 996 (D.C.1989)).
“The trial judge ... has discretion in determining whether particular evidence is relevant to bias or motive.” White v. State, 324 Md. 626, 598 A.2d 187, 194 (1991) (quoting McCoRmick on Evidence, supra, § 40, at 87). Indeed, the trial court has “a great deal of discretion” in making this determination. Id. “[T]he burden of showing the relevance of particular evidence to the issue of bias rests on its proponent.” Chambers v. State, 866 S.W.2d 9, 26-27 (Tex.Crim.App.1993). Moreover, “not everything tends to show bias, and courts may exclude evidence that is only marginally useful for this purpose.” State v. Lanz-Terry, 535 N.W.2d 635, 640 (Minn.1995). “Evidence tending only slightly to prove bias may be admitted; however, rejecting such evidence is within the discretionary power of the trial court.” State v. Jackson, 340 N.C. 301, 457 S.E.2d 862, 870 (1995).
“Proportionality is of consummate importance in judicious adjudication,” Allen v. United States, 603 A.2d 1219, 1227 (D.C.1992) (en banc), and, as the foregoing authorities demonstrate, the principle that the preclusion of all cross-examination regarding a witness’ possible bias violates the Constitution must be applied with a measure of common sense. Trivial motivations are insufficient. If Jones accidentally steps on Smith’s toe and momentarily inflicts a little pain on Smith’s corn, this might reasonably provide a motive for Smith to curse Jones or even to push him, but no reasonable person would view it as a motive to throw acid into Jones’ eyes or to shoot Jones through the heart. The present case may not be as extreme as the foregoing hypothetical, but an expression of dissatisfaction with Coles’ role in the discrimination proceeding in which Goodwine was merely a witness reasonably appeared to the trial judge to provide a very unpersuasive motive indeed for helping to frame a man for armed robbery by fabricating a five-year-old sale of a handgun.6 Athough the judge did not *491express herself in precisely these terms, we are satisfied that this is what she was driving at. To articulate the point by resort to this court’s language in Barnes, supra, the defense proffer did not amount to the “specific personal bias,” 614 A.2d at 905, required to lay a foundation for cross-examination for bias. The proffer of bias was marginal at best, and thus quite inadequate to require the judge to permit the proposed line of inquiry. Cf. Lanz-Terry, supra, 535 N.W.2d at 640; Jackson, supra, 457 S.E.2d at 870.
Moreover, the situation before the trial judge was rife with the potential for confusion of the issue and for distraction of the jury from the question whether Coles was innocent or guilty:
Impeachment is not a dispassionate study of the capacities and character of the witness, but is regarded in our tradition as an attack upon his credibility. Under our adversary system of trials the opponent must be given an opportunity to meet this attack by evidence sustaining or rehabilitating the witness.
McCormick on Evidence, supra, § 49, at 115 (emphasis in original). Accordingly, if the trial judge had permitted the line of inquiry proffered by the defense, the prosecution would have had the right to rehabilitate Goodwine, and would presumably have done so by attempting to show that his comments about Coles were accurate and justified and did not reflect bias against the defendant. The inquiry would then have been diverted from the question of Coles’ innocence or guilt to the merits of a collateral dispute between Goodwine and Coles which arose in the context of a discrimination case. It is no secret that allegations of unlawful discrimination tend to capture one’s attention, and the proposed cross-examination would have had a significant potential for distracting of the jury. Under these circumstances, we perceive no legal error or abuse of discretion on the trial judge’s part.7
III.
CONCLUSION
For the foregoing reasons, Coles’ convictions are hereby
Affirmed.
. D.C.Code §§ 22-2901, -3202 (1996), recodi-fied as D.C.Code §§ 22-2801, -4502 (2001).
. D.C.Code § 22-3204(b), recodified as D.C.Code § 22-4504(b) (2001).
. Coles was acquitted of armed robbery and related weapons charges in relation to the other two incidents that were charged in the indictment.
. Coles’ remaining claims warrant little discussion. He argues that his convictions for *488armed robbery and PFCV merge, but we have previously rejected this contention. See Hanna v. United States, 666 A.2d 845, 856 (D.C.1995) ("The [PFCV] count does not merge with . .. the armed robbery count”); Thomas v. United States, 602 A.2d 647, 650 (D.C.1992) ("[T]he Council [of the District of Columbia] did not intend ... the offense [of PFCV] to merge with an offense subject to the enhanced penalty provision of [D.C.Code § 22-]3202.”).
Coles also complains that, in reinstructing the jury with respect to the elements of armed robbery, the trial judge omitted the definition of the words "carried the property away.” The element itself was not omitted from the reinstruction, and the judge had previously instructed the jury as to the meaning of the language in question.
Coles’ attorney did not object to the rein-struction. Rule 30 of the Superior Court's Rules of Criminal Procedure provides in pertinent part:
No party may assign as error any portion of the charge or omission therefrom unless that party objects thereto before the jury retires to consider its verdict, stating distinctly the matter to which that party objects and the grounds of the objection.
Under these circumstances, we review only for plain error, Johnson v. United States, 520 U.S. 461, 466-67, 117 S.Ct. 1544, 137 L.Ed.2d 718 (1997), and find none.
. We cannot agree with our dissenting colleague that the quoted language rises to the level of an "expression] [of] animus” against Coles. Post at 491. Indeed, in our view, phrases like "animus” and "demonstrabl[e] bias,” id. at 493, overstate the reality when one considers that we are dealing here with an alleged motive for falsely associating Coles with an armed robbery. See infra, pp. 490-91.
. According to our dissenting colleague, it was unnecessary for the defense to show that "the proffered bias was of a magnitude which would cause Goodwine to assist in 'framing’ appellant.” Post, p. 494. But surely an impartial jury could not rationally conclude that Goodwine mistakenly believed that he had sold Coles a handgun, or that Goodwine believed that he knew the serial number of the weapon when he did not. On this record, Goodwine was either telling the truth or he intentionally framed Coles for an armed robbery, and the judge reasonably concluded that Coles had not proffered evidence of the kind of bias which could reasonably lead the jury to believe that such deliberate framing had occurred.
Judge Ruiz also suggests, id., that reversal is warranted even though there was no "need to doubt that Goodwine sold a gun to appellant at some time while they worked together for the Marine Corps.” (Emphasis in original.) Her hypothesis seems to be that although Coles purchased a weapon from Goodwine, Coles’ discrimination suit could have so angered Goodwine that he would provide a false serial number for the weapon he sold to Coles just to inculpate Coles in an armed robbery. We are satisfied that this possibility is sufficiently remote to ensure that no impartial jury would reasonably believe it, and the judge could reasonably so conclude.
. The judge evidently thought it implausible, and so do we, that Goodwine would fabricate the sale of a handgun five years earlier in order to retaliate in such a devastating way against Coles’ actions in the discrimination case. We do not read the dialogue between court and counsel quoted in footnote 1 of the dissent as being based primarily on the lapse of time since the alleged sale. On the contrary, the notion that Goodwine would invent so old a transaction was simply one of several factors showing the improbability of the defense’s entire “motive to fabricate” theory.