delivered the Opinion of the Court.
Both Speer and the People petitioned for review of the court of appeals' judgment reversing Speer's conviction for attempted aggravated robbery. See People v. Speer, 216 P.3d 18 (Colo.App.2007). The People sought review of the court of appeals' determination that the district court erroneously denied Speer's requested jury instruction on the affirmative defense of duress, resulting in the reversal of his conviction. Speer cross-petitioned, asserting that even if this court were to disagree that denial of his requested instruction was reversible error, he would nevertheless be entitled to a new trial because the district court erred in rejecting his challenges for cause to two prospective jurors who worked in airport security.
Because there was simply no evidence from which a reasonable jury could find that the defendant acted under duress, as the statute defining that defense has been construed by this court, the district court did not err in rejecting the defendant's proffered duress instruction. Because neither the Department of Homeland Security (DHS) nor the Transportation Security Administration (TSA) is a public law enforeement agency within the meaning of subsection 16-10-103(1)(k), C.R.S. (2010), the district court also did not err in rejecting the defendant's challenges for cause to the two jurors in question. The judgment of the court of appeals is therefore reversed, and the case is remanded with directions to reinstate the judgment of conviction.
1.
Tremaine D. Speer was charged with attempt to commit first degree murder, first *1118degree assault, attempt to commit aggravated robbery, theft by receiving, possession of a weapon by a previous offender, and committing a crime of violence, all arising from an attempted robbery and shooting of the robbery victim outside a convenience store on April 6, 2004. The jury convicted Speer of attempted aggravated robbery and committing a erime of violence, but it acquitted him of both attempted murder and first degree assault.1 He was sentenced to a term of incarceration of sixteen years.
During the jury selection process, the defense challenged two prospective jurors for cause when they indicated that they worked in airport security for the Department of Homeland Security.2 The defendant argued that they were employees of a public law enforcement agency, as contemplated by subsection 16-10-103(1)(k) of the revised statutes. The trial court denied both challenges on the ground that security screeners, like the two prospective jurors in question, could not be considered employees of a public law enforcement agency subject to challenge for cause. Speer exercised a peremptory challenge to remove one of the prospective jurors but exhausted his remaining peremptory strikes before questioning the second juror, who therefore sat for the trial.
At trial, the prosecution presented evidence that the victim negotiated with an acquaintance named Jamar Dickey to sell his used Honda for $600. After the victim met Dickey at an automotive parts store on the evening in question and completed the vehicle transaction, Dickey agreed to drive him and his family home in the Honda. When Dickey made an unplanned stop at a convenience store and went inside, Speer emerged from behind a dumpster in the parking lot, pointed a gun at the victim, and demanded his money. As the victim hesitated, Speer shot the victim in the stomach. After a brief altercation with Speer, the victim fled on foot and collapsed less than a block from the convenience store.
Testifying on his own behalf, Speer did not dispute that he demanded the victim's money at gunpoint or that he shot the victim in the process but asserted instead that the shooting was accidental and that the robbery was part of a plot in which he participated only under duress. Speer testified that the man identified as Dickey, an acquaintance whom Speer had met through friends several months before, threatened him with a gun earlier in the day and also threatened to find and harm his brother if he declined to cooperate in the robbery. He described in considerable detail the entire day he spent with Dickey, including various times in which he was out of Dickey's presence and in control of both Dickey's gun and a car. In particular he described positioning himself to carry out the robbery by driving himself, with the weapon in his possession, to the alley behind the convenience store, while Dickey was meeting the victim at the automotive parts store to consummate the sale.
At the close of evidence Speer requested that the jury be instructed on the affirmative defense of duress. The trial court, however, denied the instruction, finding that Speer had failed to present evidence from which the jury could make the factual findings necessary to satisfy the defense.
The court of appeals reversed, concluding that sufficient evidence of the defense had been presented at trial,. In its opinion, the division held that the imminence of a threat is a question for the jury in all but the clearest of cases and that Dickey's threats to harm Speer's brother, if believed by the jury, were sufficient to support a finding that he lacked any reasonable opportunity to escape. See Speer, 216 P.8d at 24. The court of appeals, however, rejected Speer's argument that the district court erred in declining to sustain his challenges for cause to prospective jurors working as airport security screeners. See id. at 25-26.
We granted the People's petition for a writ of certiorari challenging the court of appeals' reversal for rejecting the defendant's pro*1119posed duress instruction, as well as Speer's cross petition challenging the decision to permit airport security personnel to sit.
IL.
It is too well settled to merit further discussion that a trial court is obliged to instruct the jury on a requested affirmative defense if there is any credible evidence, including even highly improbable testimony of the defendant himself, supporting it. Seq, e.g., Lybarger v. People, 807 P.2d 570, 579 (Colo.1991). To place the defense in issue, however, there must be some credible evidence to satisfy each of its components or constituent elements. Id. And whether there is credible evidence to support each element of an affirmative defense is a question for the court rather than the jury. Id. Similarly, the construction of a statute defining an affirmative defense, and consequently the determination of the precise elements of that defense, is a question of law for the court. See People v. Garcia, 118 P.3d 775, 780 (Colo.2005).
This jurisdiction has long codified some version of the related common law defenses of duress and necessity. See §§ 18-1-702, -708, CRS. (2010), C.R.S.1963, §§ 40-1-802, -808 (1971 Perm. Cum. Supp.); see also United States v. Bailey, 444 U.S. 394, 410, 100 S.Ct. 624, 62 L.Ed.2d 575 (1980) (discussing the common law defenses and some of their more modern variations and codifications). Our current statutory defense of duress bars the conviction of a person for any criminal offense, other than a class 1 felony, "based upon conduct in which he engaged at the direction of another person because of the use or threatened use of unlawful foree upon him or upon another person, which foree or threatened use thereof a reasonable person in his situation would have been unable to resist." § 18-1-708. While this statute no longer expressly limits the applicability of the defense to threats of death or serious bodily injury, neither does it expand the defense so far as to include every threat causing subjective fear or exculpate every defendant too weak to resist threats against himself or another. See Bailey v. People, 680 P.2d 1062, 1068-69 (Colo.1981); see also People v. Preciado-Flores, 66 P.3d 155, 163 (Colo.App.2002) (fear must be "well-grounded"); People v. Robertson, 36 Colo.App. 367, 369, 548 P.2d 533, 585 (1975). The statute retains an objective standard of reasonableness, exculpating only for threats that a reasonable person would not have been able to resist.
Defenses of necessity, whether occurring in more generic forms like choice of evils or duress, or more specific incarnations like defense of person, property, or premises, have never been available as alternatives to relying on the protection of the law. See generally 2 Wayne R. LaFave, Substantive Crimi nal Law § 9.1(a), at 7 (2d ed. 2008) (stating that justification defenses generally are unavailable where there is "some opportunity to seek less drastic means of avoiding that harm"). In characterizing the common law defenses of duress and necessity in particular, the United States Supreme Court has noted that "[ulnder any definition of these defenses one principle remains constant: if there was a reasonable, legal alternative to violating the law, a chance both to refuse to do the criminal act and also to avoid the threatened harm, the defenses will fail." Bailey, 444 U.S. at 410, 100 S.Ct. 624 (quoting Wayne R. LaFave & Austin W. Scott, Handbook on Criminal Law § 49, at 379 (1972)).
We have consistently construed our own statute, with its requirement that the threatened force exeeed any objectively reasonable ability to resist, as making the defense of duress, like the closely related defense of necessity or choice of evils, unavailable in the absence of a specific and imminent threat of injury under cireumstances leaving the defendant no reasonable alternative other than to violate the law for which he stands charged. See Bailey, 630 P.2d at 1068; People v. Handy, 198 Colo. 556, 559, 608 P.2d 941, 948 (1979); accord People v. Trujillo, 41 Colo.App. 223, 225, 586 P.2d 235, 237 (1978); Robertson, 36 Colo.App. at 369, 543 P.2d at 535; cf People v. Strock, 623 P.2d 42, 44 (Colo.1981) (choice of evils). And in a variety of settings, we have found it proper for courts to deny an instruction on one or the other of these related defenses based on the *1120existence of undisputed evidence of reasonable legal alternatives. See, eg., People v. Smith, 754 P.2d 1168, 1170 (Colo.1988) (rejecting self-defense instruction where defendant's act of shooting victim's car not reasonably "necessary to defend himself"); Handy, 198 Colo. at 559-60, 608 P.2d at 948 (rejecting choice-of-evils instruction where escaped prisoner failed to report once imminent threat had dissipated); accord People v. Laurson, 15 P.3d 791, 795 (Colo.App.2000) (rejecting self-defense instruction where victims were already fleeing); People v. Suazo, 867 P.2d 161, 169 (Colo.App.1998) (rejecting defense-of-others instruction where victim had already left fracas to seek medical attention).
Taking all of Speer's testimony as true, the record was nevertheless devoid of any evidence to support a finding that Dickey's threats were sufficiently imminent to strip him of any reasonable legal alternative to committing robbery at gunpoint and, as it turned out, shooting and seriously wounding the victim. By Speer's own account, he and Dickey spent the day together after Dickey's initial threats, at various points during which Speer was either in sole possession of Dickey's gun or completely out of Dickey's presence. Most particularly, Speer testified that he was left in control of both a vehicle and Dickey's gun while Dickey consummated the purchase of the victim's Honda at the auto parts store, and that while the sale was occurring, he chose to drive to the scene of the robbery and lie in wait for Dickey and the victim, rather than flee and report Dickey's threats and intentions to the police. See United States v. Johnson, 416 F.3d 464, 466, 468-69 (6th Cir.2005) (upholding refusal to submit duress instruction where accomplice voluntarily handed defendant his only weapon to enable defendant to commit planned crime); State v. Charlton, 338 N.W.2d 26, 31 (Minn.1983) (duress defense adequately disproved where defendant had opportunity to take possession of gun from alleged threatening accomplice but failed to do so).
Notwithstanding these opportunities to seek police protection and foil the robbery plot, the court of appeals felt that Speer's otherwise criminal conduct could nevertheless be justified by Dickey's threats against Speer's brother. But unlike a hostage situation or other cireumstance of immediate danger to someone else, there was no suggestion that Speer's brother was at any time under the control of either Dickey or an accomplice. Speer testified only that he feared Dickey would later find and hurt him or his brother unless he assisted with the robbery. It was not for the jury to decide whether the defendant was justified in not placing his faith in the legal system onee he had a clear opportunity to do so. See People v. Brandyberry, 812 P.2d 674, 679 (Colo.App.1991). (disapprovy-ing choice-of-evils instruction where defendants failed to seek assistance of law enforcement officials after abducting victim from cult).
Unless a jury were presented with evi-denee from which it could find that given the imminence of the threat, violation of the law was the defendant's only reasonable alternative, he could not be entitled to a duress instruction. Where, as here, the defendant's own account alleges only threats of remote or future injury, made under circumstances revealing present opportunities to notify law enforcement and seek their protection without immediate risk to himself or his brother, the defense of duress was unavailable as a matter of law. The district court therefore properly denied the requested instruction.
IIL.
By both statute and rule, a criminal trial court is obligated to sustain a challenge for cause to any prospective juror who is a compensated employee of a public law enforcement agency3 See § 16-10-108(1)(k); Crim. P. 24(b)(1)(XI1) (similar language but without expressly requiring compensation). On their face, the statute and rule express concern for the nature of the employing agency rather than the specific duties of the venireman in question, and therefore the fact *1121that the job description of any particular venireman may not directly involve law enforcement functions is not dispositive of his ability to sit. See People v. Coleman, 844 P.2d 1215, 1218 (Colo.App.1992); People v. Manners, 708 P.2d 1391, 1392 (Colo.App.1985); People v. Maes, 43 Colo.App. 365, 367, 609 P.2d 1105, 1107 (1979); People v. Scott, 41 Colo.App. 66, 68, 583 P.2d 989, 941-42 (1978). By the same token, however, a prospective juror's governmental employer does not become a public law enforcement agency solely because the prospective juror in question, or any other of his co-employees for that matter, performs law enforcement functions. See Ma v. People, 121 P.3d 205, 211 (Colo.2005) (Department of Defense not a public law enforcement agency despite overseeing the Army Military Police Corps); see also People v. Simon, 100 P.3d 487, 491 (Colo.App.2004) (Environmental Protection Agency not a public law enforcement agency despite having incidental penal law enforcement authority).
As we have noted elsewhere, the revised statutes themselves identify a number of public offices as law enforcement agencies, including, for example, any police department, sheriff's department, or district attorney's office; the office of the state attorney general; the Colorado bureau of investigations; and the Colorado state patrol. See Ma, 121 P.3d at 211. Using these designated governmental bodies as examples or prototypes, we have inferred that the legislature intended to include within the category of public law enforcement agency only agencies enforcing the criminal law, and we have interpreted the statutory designation to include not only those agencies specifically identified but also other agencies performing similar functions. See, eg., id. at 211-12 (including Army Military Police Corps). We have not, however, expanded the rubric of law enforcement agency to the extent of including any division of government whose primary purpose or mission is not the enforcement of the criminal law. E.g., id.
In the absence of an express statutory definition of the term "agency," we have interpreted it flexibly, in accordance with common usage. See id. at 210. In Ma, we explained that the term "agency" is not confined by bureaucratic happenstance and should not be interpreted rigidly so as to undermine the rationale behind the statute's rule requiring automatic disqualification. Id. at 212 (construing "agency" to include a "branch" of the Army). We there made no attempt to limit the applicability of the term in any formal way to governmental bodies of a certain level or with specific authority concerning ultimate employment determinations. Quite the contrary, we made clear in Ma that an "agency" for purposes of the statute may be either a division of government or some smaller subdivision of a larger governmental agency. Id.
As a result, even though the primary function or purpose of a broader governmental organization, department, division, or agency may not be appropriately characterized as the enforcement of the criminal law, law enforcement may nevertheless be the primary function or purpose of some smaller unit or subdivision of that governmental organization. It may therefore be, and typically is, the case that although a governmental department or agency is not a public law enforcement agency within the contemplation of the statute and rule, a narrower unit or subdivision of that department is. In that event, although all of the employees of the broader governmental department are not subject to challenge for cause, those of its employees serving in a qualifying subdivision are subject to removal on the basis of their employment.
Finally, unless a public agency has already been identified as a public law enforcement agency by statute or the published case law of the jurisdiction, a trial court cannot be expected to divine its nature as a law enforcement agency without having its primary function or purpose brought to the attention of the court. It is therefore incumbent upon any party asserting a challenge for cause under this subsection of the statute not only to make timely objection but to provide the court, through examination of the prospective juror or request for judicial notice, with adequate evidence of the nature of the employing unit in question. CL People v. Topping, 764 P.2d 869, 870 (Colo.App.1988) *1122(holding State Department Administration not a public law enforcement agency because "[tlhere was no evidence" in record to that effect).
By these standards, there can be no doubt that neither the Department of Homeland Security nor the Transportation Safety Administration is a public law enforcement agency within the contemplation of the statute. Neither agency has as its predominant purpose or mission the enforcement of penal laws. Rather, both agencies are statutorily organized and authorized to protect national security. See 6 U.S.C. § 111(b)(1) ("The primary mission of [DHS] is to ... prevent terrorist - attacks within the - United States. ..."); 49 U.S.C. § 114(d) (TSA Under Secretary responsible for "security in all modes of transportation"). Such security functions do not involve the traditional law enforcement functions we identified in Ma, like the investigation of crime, or the arrest, prosecution or detention of criminal suspects. See 6 U.8.C0. § 111(b)(2) ("[Primary responsibility for investigating and prosecuting acts of terrorism shall be vested not in [DHS], but rather in Federal, State, and local law enforcement agencies with jurisdiction over the acts in question.").
Nor did anything before the district court suggest that the airport security screeners in question served in a unit or subdivision of the Administration with traditional law enforcement authority. In response to questioning by the court, both of the prospective jurors denied having any authority to detain or make arrests. One indicated that if an arrest were required, the Denver Police Department would be called, and the other made clear her belief that her position as an airport sereener did not involve any formal relationship with a law enforcement agency. Neither juror gave the slightest indication that their employing unit prosecuted suspected criminals, and Speer asked no follow-up questions.
Even if special units within the Department or Administration, like the Office of the Inspector General and Federal Air Mar-shalls, having authority to carry firearms, make arrests, and seek and execute warrants, see 5 U.S.C. app. 8, § 6(e)(1)(A)-(C); 49 U.S.C. §§ 44903(d), 44917, could be appropriately characterized as public law enforcement agencies, their status would not affect the classification of the broader agencies of which they are sub-divisions or sub-agencies. Just as our characterization of the Military Police Corps as a law enforcement agency did not require similar characterization of the United States Army or the Department of Defense, see Ma, 121 P.8d at 211-12, so too the characterization of, for instance, the Department's Office of the Inspector General as a law enforcement agency would not lead to a similar characterization of the entire Department or Transportation Safety Administration.
IV.
Because there was no evidence of the statutory defense of duress as construed by this court, and because neither DHS nor TSA is a public law enforcement ageney for purposes of subsection 16-10-108(1)(k), the judgment of the court of appeals is reversed, and the case is remanded with directions to reinstate the judgment of conviction.
Justice MARQUEZ dissents, and Chief Justice BENDER and Justice MARTINEZ join in the dissent.. On the remaining counts, Speer pled guilty pretrial to theft by receiving and the prosecution dismissed the count for possession of a weapon by a previous offender.
. One of the prospective jurors stated she worked for both DHS and TSA. TSA is currently a division within DHS. See Francis v. Mineta, 505 F.3d 266, 268 n. 2 (3d Cir.2007).
. Subsection 16-10-103(1)(k) states, "'The court shall sustain a challenge for cause on one or more of the following grounds: ... (k) The juror is a compensated employee of a public law enforcement agency or a public defender's office."