PUBLISH UNITED STATES COURT OF APPEALS FOR THE TENTH CIRCUIT

_____________________________________ W. CLARK APOSHIAN, Plaintiff - Appellant,

v. WILLIAM BARR, Attorney General of the United States; UNITED STATES DEPARTMENT OF JUSTICE; THOMAS E. BRANDON, Acting Director Bureau of Alcohol Tobacco Firearms and Explosives; BUREAU OF ALCOHOL TOBACCO FIREARMS AND EXPLOSIVES, Defendants - Appellees.

------------------------------ CATO INSTITUTE AND FIREARMS POLICY COALITION; DUE PROCESS INSTITUTE, Amicus Curiae. No. 19-4036

_________________________________ Appeal from the United States District Court for the District of Utah (D.C. No. 2:19-CV-00037-JNP-BCW)

_________________________________ Caleb Kruckenberg, Litigati on Counsel (Steve Simpson a nd Harriet Hage man, Senior Litigation Counsel; and Mark Ch enoweth, General Counsel, w ith him on the briefs), New Civil Liberties Alliance, Washingt on, DC, appearing for Appellant. Brad Hinshelwood, Attorney, Civil Division, United States Department of Justice, Washington, DC (Joseph H. Hunt, Assistant Attorney General, Civil Division, United FILED United States Court of Appeals Tenth Circuit 

### May 7, 2020 Christopher M. Wolpert Clerk of Court2 States Department of Justice, Washington, DC; John W. Huber, Un ited States Attorney, Office of the United States Atto rney for the District of Utah , Salt Lake City, Utah; Mark B. Stern, Michael S. Raab, and Abby C. Wri ght, Attorneys, Civil Division, United States Department of Justice, Washington, DC, with him on the briefs), appearing for Appellees. Ilya Shapiro, Washington, DC, fo r Amicus Curiae Cato Institute. John D. Cline, San Francisco, California, for Amicus Curiae Due Process Institute.

_________________________________ Before BRISCOE , MORITZ , and CARSON , Circuit Judges.

_________________________________ BRISCOE , Circuit Judge.

_________________________________ Plaintiff-Appellant W. Clark Aposhian ha s filed an interlocutory appeal from the district court’s denial of his motion for a preliminary injunction. The district court concluded that Mr. Aposhian had not shown a likelihood of success on the merits of his challenge to a rule promulgated by the Bu reau of Alcohol, Tobacco, Firearms, and Explosives (ATF) that classifies bump st ocks as machine guns under the National Firearms Act (NFA), 26 U.S.C. §§ 5801–5872. See Bump-Stock-Type Devices, 83 Fed. Reg. 66,514 (Dec. 26, 2018) (F inal Rule). The Final Rule was promulgated to clarify the definition of “machinegun” as fo und in 26 U.S.C. § 5845(b). 1 It is that definition of machine gun and the Final Rule that are the fo cus of this appeal. Exercising jurisdiction pursuant to 28 U.S.C. § 1292(a )(1), we agree with the outco me reached by the district court that Mr. Aposhian has failed to establis h a likelihood of success on the merits of his challenge to the Final Rule, and we affirm the denial of preliminary injunctive relief.

1 We use the two-word spelling of mach ine gun except when quoting sources.3 I Statutory Framework The NFA (i) regulates the pr oduction, dealing in, possessi on, transfer, import, and export of covered firearms; ( ii) creates a national firearms registry; and (iii) imposes taxes on firearms importers, manufacturers, and dealers, as well as specified transfers of covered firearms. 26 U.S.C. §§ 5801–5861. Failure to comply with the NFA’s requirements results in penalties and forfeiture and subjects the violator to the general enforcement measures available u nder the internal revenue laws. Id. §§ 5871–5872. “Machinegun[s]” are subject to regulatio n and registration under the NFA. Id. § 5845(a). The NFA defines a “machinegun” as “any weapon which shoots, is designed to shoot, or can be readily re stored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger.” Id. § 5845(b). The definition also includes “the frame or receiver of any such weapon,” as well as “any part” or “combination of parts designed and intended , for use in converti ng a weapon into a machinegun,” and “any co mbination of parts from which a machinegun can be assembled” as long as those “parts are in th e possession or under the control of a person.” Id. Congress expressly charged the Attorney General with the “administration and enforcement” of the NFA, id. § 7801(a)(1), (a)(2)(A), and pr ovided that the Attorney General “shall prescribe all needful rules an d regulations for the enforcement of” the NFA, id. § 7805; see id. § 7801(a)(2)(A).4 The Gun Control Act of 1968 (GCA), 18 U. S.C. § 921 et seq ., as amended by the Firearm Owners’ Protection Act, Pub. L. No. 99-308, 100 Stat. 449 (1986), imposes both criminal prohibitions and a regulatory licensing scheme on certain firearm transactions.
See 18 U.S.C. § 922 (criminal prohibitions); id. § 923 (licensing scheme). The GCA incorporates by reference the defin ition of machine gun in the NFA. See id. § 921(a)(23). The GCA also expressly delegates administrative and rulemaking authority to the Attorney General to “prescribe only such rules and regulations as are necessary to carry out the provisions of this chapter.” Id. § 926(a). The Attorney General has delegated the responsibility for enforcing and admi nistering the NFA and the GCA to ATF. See 28 C.F.R. § 0.130(a). Under 18 U.S.C. § 922(o), it is “unlawfu l for any person to transfer or possess a machinegun.” Conversely, many firearms requiring a distinct pull of the trigger to shoot each bullet are lawful. See generally id. § 922; 26 U.S.C. § 5845. Over time, ATF has promulgated regulations and issued rulings defining various terms in the NFA and GCA and classifying weapons a nd parts as machine guns. Regulation of Bump Stocks A “bump stock” is a device that replace s the standard stationary stock of a semiautomatic rifle—the part of the rifle that generally rests against the shooter’s shoulder—with a sliding, non-stationary stock that permits the shooter to rapidly increase the rate of fire, approximating that of an automatic weapon. Final Rule at 66,516. A bump stock does so by chan neling the recoil energy from each shot “into the space created by the sliding stock (approximately 1. 5 inches) in constrained linear rearward and5 forward paths.” Id. at 66,518. The bump stock “harnesse s the firearm’s recoil energy as part of a continuous back-and-forth cycle that allows the shooter to attain continuous firing” following a single pull of the trigge r, producing a rapid bumping of the trigger against the shooter’s stationary finger. Id. at 66,533. That design allows the shooter, by maintaining constant rearward pre ssure on the device’s extension ledge 2 with the trigger finger as well as forward pressure on the front of the gun, to fire bullets continuously and at a high rate of fire to “mimic automatic fire.” Id. at 66,516. This continuous cycle of fire-recoil-bump-fire lasts until the shooter re leases the trigger by removing his finger from the extension ledge, the weapon malfunc tions, or the ammunition is exhausted. Id. at 66,519. The Attorney General, exercising his regulatory authority, first included a bump stock device—the Akins Accelera tor—within the statutory definition of “machinegun” in
2006. See ATF Ruling 2006-2; see also Akins v. United States , 312 F. App’x 197, 199 (11th Cir. 2009). The Akins Accelerator, unlik e many bump stocks, used “an internal spring” to “reposition and refire” the firearm. Akins , 312 F. App’x at 198. ATF later limited the devices it defined as machine guns by concluding that bump stocks that operated without an internal spring were not machine gu ns. Final Rule at 66,514. On October 1, 2017, a shoo ter in Las Vegas, Nevada, used multiple semiautomatic rifles equipped with bump stoc ks to fire several hundred rounds of ammunition into a

2 The extension ledge or “finger rest” is where the “shooter places the trigger finger while shooting the firearm.” Final Rule at 66,516.6 crowd of concert attendees with in a short period of time. Id. at 66,516. 3 The “‘rapid fire’ operation” of the shooter’s weapons enable d by the bump stocks left 58 dead and approximately 500 wounded. Id. In response, President Tr ump directed the Department of Justice “to propose for notice and comment a rule banning all devices that turn legal weapons into machineguns.” Application of the Definition of Machinegun to “Bump Fire” Stocks and Other Similar Devices, 83 Fed. Reg. 7,949, 7,949 (Feb. 20, 2018). ATF then revisited the status of bump stocks, re viewed its earlier determinations for bumpstock-type devices issued between 2008 and 2017, and decided to clarify by the rulemaking process the statutory terms “au tomatically” and “single function of the trigger” as applied in defining what is or is not a machine gun. Final Rule at 66,514– 66,515. On March 29, 2018, th en-Attorney General Sessions issued a Notice of Proposed Rulemaking that suggested “amend[ing] the [ATF] regulations to clarify that [bump stocks] are ‘machineguns’” un der 26 U.S.C. § 5845(b). See Bump-Stock-Type Devices, 83 Fed. Reg. 13,442 (March 29, 2018). ATF promulgated its Final Ru le on December 26, 2018. Regarding the statutory definition of machine gun, the Final Rule pr ovided that the NFA’s use of “the term ‘automatically’ as it modifies ‘shoots, is desi gned to shoot, or can be readily restored to shoot,’” 26 U.S.C. § 5845(b), “m eans functioning as the result of a self-acting or self3 Because ATF had not regulated certain t ypes of bump stocks under the NFA or GCA, they were not marked with a serial nu mber or other identification markings. As a result, individuals were able to legally purchase bump stocks without undergoing background checks or co mplying with any other federa l regulations applicable to firearms. Final Rule at 66,516.7 regulating mechanism that allows the firing of multiple rounds through a single function of the trigger.” Final Rule at 66,553–66,554 (codified at 27 C.F.R. §§ 447.11, 478.11, 479.11). The Final Rule further defined “s ingle function of the trigger,” 26 U.S.C. § 5845(b), to mean “a single pull of the trigge r and analogous motions.” Final Rule at 66,553–66,554 (codified at 27 C.F.R. §§ 447.11, 478.11, 479.11). Given those definitions, the Final Rule concluded that the statutory term “‘machinegun’ includes a bump-stock-type de vice”—that is, “a device that allows a semiautomatic firearm to shoot more than one shot with a single pull of the trigger by harnessing the recoil energy of the semiautomatic firearm to wh ich it is affixed so that the trigger resets and continues firing without ad ditional physical manipul ation of the trigger by the shooter.” Id. (codified at 27 C.F.R. §§ 447.11, 478.11, 479.11). For its authority to promulgate the Fi nal Rule, ATF relied on both the “plain meaning” of the NFA and the A ttorney General’s delegation to the agency to administer and enforce the NFA and GCA. Id. at 66,527. In addition, ATF stated that if 26 U.S.C. § 5845(b) is ambiguous, the Final Rule “rests on a reasonable construction.” Id. (citing and invoking Chevron U.S.A., Inc. v. Nat. Res. Def. Counsel , 476 U.S. 837 (1984)). ATF explained that although Congress defined “m achinegun” in the NFA, “it did not further define the components of that definition . . . Congress thus imp licitly left it to the [Attorney General] to define ‘automatically ’ and ‘single function of the trigger’ in the event those terms are ambiguous.” Id. ATF stated that the Final Rule would become “effective” on March 26, 2019, ninety days after promulgation. Id. at 66,514. ATF stated further that individuals would8 be subject to “criminal liability only for possessing bump-stock-type devices after the effective date of regulation, not for possession before that date.” Id. at 66,525. Bumpstock owners were directed to destroy their devices or leave them at an ATF office by March 26, 2019. Id. at 66,514. Procedural History Mr. Aposhian purchased a Slide Fire bump stock before the Final Rule was promulgated. He filed suit against vari ous governmental officers and agencies challenging the Final Rule as unconstitutiona l and in violation of the Administrative Procedure Act (APA), arguing that the Final Ru le contradicts an unambiguous statute, 26 U.S.C. § 5845(b), and mistaken ly extends its statutory defi nition of “machinegun” to cover bump stocks. The government also ar gued the statute is unambiguous but that the Final Rule is merely interpretive and, as so, re flects the best interpretation of the statutory text. For its part, the district court did no t specifically opine on whether the statute was ambiguous or not. Ultimately, the district court denied Mr. Aposhian’s motion for a preliminary injunction, concluding th at because the Final Rule repres ented the best reading of the statute, Mr. Aposhian was not likely to suc ceed on the merits of his challenge. Aplt. App. at 181. Because it concluded that Mr. Aposhian was unlikely to succeed on the merits, the district court did not reach the other three preliminary-injunction factors. See id. at 175. Mr. Aposhian filed a notice of ap peal and sought an in junction pending appeal from this court, which was denied. Id. at 226.9 II We review the district court’s denial of a preliminary injunction for abuse of discretion. Wilderness Workshop v. BLM , 531 F.3d 1220, 1223 (10th Cir. 2008). “An abuse of discretion occurs ‘only when the tr ial court bases its de cision on an erroneous conclusion of law or where there is no rationa l basis in the evidence for the ruling.’” Utah Licensed Beverage Ass’n v. Leavitt , 256 F.3d 1061, 1065 (10th Cir. 2001) (quoting Hawkins v. City and Cty. of Denver , 170 F.3d 1281, 1292 (10th Cir. 1999)). “Thus, we review the district court’s factual findings fo r clear error and its conclusions of law de
novo.” Fish v. Kobach , 840 F.3d 710, 723 (10th Cir. 2016). “A preliminary injunction is an extrao rdinary remedy, the ex ception rather than the rule.” United States ex rel. Citizen Band Potawa tomi Indian Tribe v. Enter. Mgmt. Consultants, Inc. , 883 F.2d 886, 888 (10th Cir. 1989 ). “To obtain a preliminary injunction, the movant must show: (1) a substantial likelih ood of success on the merits; (2) irreparable harm to the movant if the in junction is denied; (3) the threatened injury outweighs the harms that the preliminary in junction may cause the opposing party; and (4) the injunction, if issued, will not a dversely affect the public interest.” Gen. Motors Corp. v. Urban Gorilla, LLC , 500 F.3d 1222, 1226 (10th Ci r. 2007). The third and fourth factors “merge” when, like here, the g overnment is the opposing party. Nken v. Holder , 556 U.S. 418, 435 (2009). “[B]ecause a preliminary injunction is an extraordinary remedy, the [movant’s] right to relie f must be clear and unequivocal.” Dominion Video Satellite, Inc. v. Echostar Satellite Corp. , 356 F.3d 1256, 1261 (1 0th Cir. 2004) (internal quotation marks omitted).10 III To obtain preliminary injunctive relief, Mr. Aposhian must demonstrate a substantial likelihood of success on the merits of his challenge to the Final Rule. While his complaint raises both constitutional and APA claims, he does not cite to any constitutional provision or section of the APA in the portion of his opening brief discussing his likelihood of success on the me rits. It is clear, however, that Mr. Aposhian’s merits arguments in this court conc ern only issues of statutory interpretation. Specifically, he contends that he has demons trated a substantial lik elihood of success on the merits because ATF’s interpretation of 26 U.S.C. § 5845(b) contradicts the unambiguous language of the statute. Aplt. B r. at 13. He also argues that because the statute is unambiguous, ATF had no authority to promulgate a rule defining its terms. Id. at 30. In the alternative, Mr. Aposhian conte nds that any ambiguity in the statute must be construed in his favor under the rule of lenity. 4 Id. at 37. 5 Because Mr. Aposhian is challenging ATF’ s authority to promulgate the Final Rule, the APA governs our review. See WildEarth Guardians v. United States Fish and

4 Under the rule of lenity, courts “interpr et ambiguous statutes . . . in favor of criminal defendants.” United States v. Gay , 240 F.3d 1222, 1232 (1 0th Cir. 2001). “The rule of lenity ‘is a rule of last resort [and] the mere asserti on of an alternative interpretation is not sufficient to bring the rule into play.’” Id. (quoting United States v. Blake , 59 F.3d 138, 140 (10th Cir. 1995)).

5 Mr. Aposhian states in a footnote in hi s reply brief that his “claim is that the Final Rule was issued in violation of Article s I, § 1, I, §7, and II, § 3, on theories related to the vesting clauses, bicameralism and pr esentment, non-divestment and separation of powers principles.” Aplt. Rep. Br. at 27 n.1 (citing his complaint). Not only does Mr. Aposhian fail to cite any caselaw suppor ting these arguments, these constitutional theories are absent from his opening brief. We routinely “decline[] to consider arguments11 Wildlife Serv. , 784 F.3d 677, 683 (10th Cir. 2015) (n oting that the APA applies “when asking whether an agency has acted within its authority”); see also Citizens’ Comm. to Save Our Canyons v. Krueger , 513 F.3d 1169, 1176 (10th Cir. 2008) (stating that the APA “governs judicial review of agency actions ”). As relevant to the arguments here, we may only set aside agency action that is “in excess of statutory jurisdiction, authority, or limitations, or short of statutor y right.” 5 U.S.C. § 706(2)(C). We conclude that Mr. Aposhian has not shown that ATF acted beyo nd its authority and has thereby failed to demonstrate a substantial like lihood of success under the APA. A At the outset, we must determine what stan dard we are to apply in addressing the Final Rule’s conclusion that bump stoc ks are “machineguns” under the statutory definition. When confronted with this questi on of statutory interpretation and what if any weight the district court should accord ATF’ s interpretation under its Final Rule, the parties seemed oddly in agr eement. Mr. Aposhian argu ed repeatedly against the application of Chevron deference, citing Chevron in his motion for a preliminary injunction to argue that ATF’s construction of the statute should be rejected, Aplt. App. at 44–45, and devoting the entirety of his repl y brief to argue the Final Rule fails under both step one and step two of Chevron , see id. at 111–19. And, as the district court noted

that are not raised, or are inadequately pr esented, in an appellant’s opening brief,” Bronson v. Swensen , 500 F.3d 1099, 1104 (10th Cir. 20 07)), and it is well settled that we do not ordinarily review issues raised for the first time in a reply brief, Sylvia v. Wisler , 875 F.3d 1307, 1332 n.7 (10th Cir. 2017). We see no reason to deviate from those principles here.12 in its memorandum opinion an d order denying the motion for a preliminary injunction, the government “went out of [its] way to avoid citing Chevron and its progeny and repeatedly stressed that [the defendants] neither request, nor believe their interpretations are entitled to, any measure of deference.” Id. at 177 n.8. In the end, the district court did not apply the Chevron framework. Id. Rather, it concluded that the Final Rule represented the best interpretation of the statute. Id. at 181. Generally, however, “we apply the test established by Chevron . . . when asking whether an agency has acted within its authority.” WildEarth , 784 F.3d at 683 (emphasizing that appellate review unde r APA § 706(2)(C) proceeds under the Chevron framework). If Chevron applies, we first ask if the st atute is ambiguous concerning whether bump stocks can be considered “m achineguns.” If so, we sustain the Final Rule’s conclusion that bump stocks are machine guns as long as the Final Rule’s conclusion is reasonable. See Entergy Corp. v. Riverkeeper, Inc. , 556 U.S. 208, 218 (2009). At this second step, an “agency need not adopt . . . the best reading of the statute, but merely one that is permissible.” Dada v. Mukasey , 554 U.S. 1, 29 n.1 (2008). On the other hand, if Chevron ’s two-step framework is inapplicable, we accept ATF’s interpretation only if it is the best reading of the statute. While the parties protest the applicability of Chevron on various grounds, we conclude that the Final Rule warrants consideration under the Chevron framework. (i) Initially, the applicability of Chevron depends on what kind of rule the Final Rule represents. There is a “central distinction” under the APA between legislative rules and13 interpretive rules. Chrysler Corp. v. Brown , 441 U.S. 281, 301 (1979); see 5 U.S.C. § 553(b), (d). Legislative rules generally receive Chevron deference, whereas interpretive rules “enjoy no Chevron status as a class.” United States v. Mead Corp. , 533 U.S. 218, 232 (2001). A legislative rule is one that “is promul gated pursuant to a di rect delegation of legislative power by Congress and . . . chan ges existing law, policy, or practice.” Rocky Mountain Helicopters, Inc. v. F.A.A. , 971 F.2d 544, 546 (10th Cir. 1992). A legislative rule affects individual rights and obligations , and, if it is “the product of certain procedural requisites,” it has th e force and effect of law. Chrysler Corp. , 441 U.S. at 301–02. An interpretiv e rule, on the other hand, “attempts to clarify an existing rule but does not change existing law, policy, or practice.” Rocky Mountain Helicopters , 971 F.2d at 546–47. An interpre tive rule simply “‘advise[s] the public of the agency’s construction of the statute and rules which it administers.’” Sorenson Commc’ns, Inc. v.
F.C.C. , 567 F.3d 1215, 1222 (1 0th Cir. 2009) (quoting Shalala v. Guernsey Mem. Hosp. , 514 U.S. 87, 99 (1995)). The government contends—and the districtcourt found—that the Final Rule is merely interpretive. See Aple. Br. at 37–38; Aplt. App. at 176. But “[t]he agency’s own label for its action is not dispositive.” Sorenson , 567 F.3d at 1223. Instead, “[t]he court must rely upon the reasoning set forth in the administrative record and disregard post hoc rationalizations of counsel.” Id. at 1221. Here, “[a]ll pertinent indicia of agency intent confirm that the [Final] Rule is a legislative rule.” Guedes v. Bur. of Alcohol, Tobacco,14 Firearms & Explosives , 920 F.3d 1, 18 (D.C. Cir. 2019) (reviewing the Final Rule under the Chevron framework). First, the Final Rule demons trates that ATF intended to change the legal rights and obligations of bump-stock owne rs. The Final Rule directed bump-stock owne rs to either destroy or surrender to ATF any bump stock in their possession and stated that “[t]he rule would criminalize only future conduct, not past possession of bump-stock-type devices that ceases by the effective date of this rule .” Final Rule at 66,525. The Final Rule announced that a person “in possession of a bump-stock-type device” in fact “ is not acting unlawfully unless they fail to relinquish or destroy their device after the effective date of this regulation.” Id. at 66,523 (emphasis added). This effort to “‘directly govern[] the conduct of members of the public, affecting individual rights and obligations’” is “powerful evidence” that AT F intended the Final Ru le to be a binding application of its rulemaking authority. Guedes , 930 F.3d at 18 (quoting Long Island Care at Home, Ltd. v. Coke , 551 U.S. 158, 172 (2007)). ATF, when promulgating the Final Rule, “f urther evinced its intent to exercise legislative authority by expressly invoking the Chevron framework and then elaborating at length as to how Chevron applies to the [Final] Rule.” Id. at 18–19 (noting that ATF’s “exegesis” on Chevron “would have served no purpose unless the agency intended the [Final] Rule to be legislative in character” ). Moreover, the Final Rule expressly invoked two separate delegations of legislative powe r, one under the NFA, 26 U.S.C. § 7805, and one under the GCA, 18 U.S.C. § 926(a). See Final Rule at 66,515. These provisions,15 according to the Final Rule, give the A ttorney General “the responsibility for administering and enforcing the NFA and GC A,” which he has delegated to ATF. Id. In addition, the Final Rule was publishe d in the Code of Federal Regulations (CFR). By statute, administrative rules publis hed in the CFR are limited to those “having general applicability and legal effect.” 44 U.S. C. § 1510. For all of these reasons, it is evident that the Final Ru le intends to speak wi th the force of law. Ordinarily, legislative rules are entitled to Chevron deference. See Sinclair Wyoming Refining Co. v. EPA , 887 F.3d 986, 991 (10th Cir. 2017). Nonetheless, the parties assert that Chevron deference is inappropriate here . Mr. Aposhian argues that Chevron deference has been waived by the g overnment because the government has disavowed any reliance on Chevron throughout this litigation. Aplt. Br. at 42–43. Next, the parties (including the government) submit that Chevron deference is inapplicable when the government inte rprets a statute that imposes criminal liability. See Aplt. Br. at 44; Aple. Br. at 40. Neither of these objections to applying Chevron are likely to succeed in the context of the Final Rule, particularly when one recalls the citation to and reliance

on Chevron when the Final Rule was promulgated. (ii) Mr. Aposhian relies on our decision in Hydro Resources, Inc. v. EPA , 608 F.3d 1131 (10th Cir. 2010), to ar gue that the government has waived any reliance on Chevron deference and that we must abide by that waiver. Aplt. Br. at 42, 43. In Hydro

Resources , we reviewed de novo the Environmenta l Protection Agency’s interpretation of a statute because “throughout the proceed ings before the panel and . . . the en banc court,16 [the agency] itself ha[d]n’t claime d any entitlement to deference.” Id. at 1146. We noted that “[i]n these circumstances, when the agency doesn’t ask for deference to its statutory interpretation, ‘we need not resolve the . . . issues rega rding deference which would be lurking in other circumstances.’” Id. (emphasis added) (quoting Estate of Cowart v. Nicklos Drilling Co. , 505 U.S. 469, 477 (1992)). Howe ver, this passage should not be read as prohibiting our application of Chevron merely on the agency ’s say so. Simply put, “need not” does not mean “may not.” Moreover, Hydro Resources did not address a scenario where, like here, a party other than the government invokes the Chevron framework. We addressed this specific scenario in TransAm Trucking, Inc. v. Admin. Review Bd. , 833 F.3d 1206, 1212 n.4 (10th Cir. 2016), and held that the Chevron framework applies, including deference at Chevron step two. The dissent in TransAm criticized the majority for making “a wholly uni nvited foray into step two of Chevron land,” id. at 1216 (Gorsuch, J., dissenting), becaus e “the only party to mention Chevron . . . was [the plaintiff], and then only in a foot note in its brief and then only as part of an argument that the statute is not ambiguous,” id. (emphasis in original). The majority nonetheless applied both steps of Chevron and gave the agency’s interpretation of the statute deference, id. at 1212, defending its application of Chevron deference by stating, “We received our invitation from TransAm [to apply the Chevron framework] in its opening brief . . . TransAm, the appellant in this matter, relied on Chevron to argue the [agency’s] construction of the [statute] should be rejected.” Id. at n.4.17 This case is akin to TransAm

. While the government has declined to invoke Chevron throughout the course of this litigation, see Aple. Br. at 16 (arguing that “plaintiff’s discussion of Chevron deference has no bearing on the disposition of this suit”), Mr. Aposhian, lik e the plaintiff in TransAm , relies on Chevron in his opening brief to argue that ATF’s construction of the statut e should be rejected. In contending that ATF’s interpretation “contradicts the statut e itself,” Aplt. Br. at 13 (capitalization omitted), Mr. Aposhian cites Chevron , arguing that the inquiry is whether the statute “‘has directly spoken to the precise question at issue,’ and, if so, ‘t hat is the end of the matter; for the court as well as the agency must give effect to the unambiguously expressed intent of Congress,’” id. at 14 (quoting Chevron , 467 U.S. at 842–43). The plaintiff in TransAm likewise cited Chevron “as part of an argument that the statute is not ambiguous” ( Chevron step one), 833 F.3d at 1216 (G orsuch, J., dissenting), yet the majority still concluded that the plaintiff pr ovided an “invitation” to apply both steps of the Chevron framework, id. at 1212 n.4. Our “i nvitation” to apply the Chevron framework in this case is even clearer than in TransAm , given that Mr. Aposhian (1) cites Chevron in the text of his opening brief rather than in a footnote; and (2) relied on Chevron in his motion for a preliminar y injunction at the district court, Aplt. App. at 44– 45, and in his motion for an injunction pending appeal, id. at 150. Because Mr. Aposhian has invoked Chevron throughout the course of this litigation, his objection to Chevron deference based on the government’s waiver is unlikely to succeed. 6

6 While Mr. Aposhian has clearly pres ented an “invitation” to apply the Chevron framework under TransAm , we note that our cases are not entirely consistent as to18 (iii) Next, the parties contend that Chevron deference is inapplicable where the government interprets a statute that imposes criminal liability. See Aplt. Br. at 44 (“‘[C]riminal laws are for courts, not for the Government, to construe.’”) (quoting Abramski v. United States , 573 U.S. 169, 191 (2014)); Ap le. Br. at 40 (same). According to Mr. Aposhian, “ATF’s rejection of deference in favor of the rule of lenity” is required by our precedent and cons titutional limitations. Aplt. Br. at 44. Mr. Aposhian also relies

on United States v. Apel , 571 U.S. 359, 369 (2014), for the proposition that “we have never held that the Government’s reading of a criminal statute is entitled to any deference.” Mr. Aposhian, however, has failed to de monstrate a likelihood of success in establishing a general ru le against applying Chevron to agency interpretations of statutes with criminal law implications. Rather, controlling precedent points in the other direction.

In Babbitt v. Sweet Home Chapter of Communities for a Great Oregon , 515 U.S. 687 (1995), the Supreme Court reviewed a regulation interpreting a term in the

whether such an invitation is necessary. Compare Am. Wild Horse Pres. Campaign v. Jewell , 847 F.3d 1174, 1187 (1 0th Cir. 2016) (describing Chevron as a “two-part standard of review ”) (emphasis added), with Hays Med. Ctr. v. Azar , --- F.3d ---, No. 17- 3232, 2020 WL 1 922595, at *13 n.18 (10th Cir. Apr. 21, 2020) (concluding that Chevron can be waived where, unlike here, its “invocati on” is merely “perfunctory and fleeting”). To the extent that Chevron is a standard of review, we would need no invitation to apply it. See Gardner v. Galetka , 568 F.3d 862, 879 (1 0th Cir. 2009) (“It is one thing to allow parties to forfeit claims, defenses, or lines of argument; it would be quite another to allow parties to stipulate or bind us to applicati on of an incorrect legal standard . . . .”); see also Guedes , 920 F.3d at 22 (“The ‘independent powe r’ to identify and apply the correct law presumably includes application of the Chevron framework when determining the meaning of a statute.”).19 Endangered Species Act (ESA), which, like the regulation in this case, carried both civil and criminal implications. The challengers argued thatChevron deference was inappropriate because the ESA included criminal penalties. See id. at 704 n.18. The Court disagreed, holding that it would defer “t o the Secretary’s reasonable interpretation” under Chevron

. Id. at 703–04. Babbitt also rejected the argument “that th e rule of lenity should foreclose any deference to the [agency’s] interpretation of the [statute] becaus e the statute includes criminal penalties.” Id. at 704 n.18. The Court reasoned, The rule of lenity is premised on two ideas: First, “‘a fair warning should be given to th e world in language that the common world will understand, of what the law intends to do if a certain line is passed’”; second, “legislatures and not courts should define criminal ac tivity.” We have applied the rule of lenity in a case raising a narrow question concerning the application of a statute that contains criminal sanctions to a specific factual dispute—whether pistols with short barrels and attachable shoulder stoc ks are short-barreled rifles— where no regulation was present

. See United States v. Thompson/Center Arms Co. , 504 U.S. 505, 517–518, and n. 9, (1992). We have never suggested that the rule of lenity should provide the standard for revi ewing facial challenges to administrative regulations whenever the governing statute authorizes criminal enforcement. Id. (emphasis added) (citation omitted). Th us, as in this case, where a regulation is at issue, and the agency (here, ATF) has both civ il and criminal enforcement authority, Babbitt suggests that Chevron , not the rule of lenity, should apply. Our circuit precedent is in accord. In NLRB v. Oklahoma Fixture Co. , 332 F.3d 1284, 1287 (10th Cir. 2003) (en banc), we noted that “it is not entirely clear exactly how the Chevron analysis is affected by the presence of criminal liability in a statute being20 interpreted by an agency.” Noneth eless, we concluded that, under Babbitt , it was appropriate to give “some deference” under Chevron to the National Labor Relations Board’s interpretation of an exception to a criminal prohibition on employer payments to labor organizations in the Labor Management Reporting Act. Id. (noting that “the degree of deference may be dependent upon considerations of the ag ency’s particular expertise and the policies implicated by th e criminal statute in question, as well as the extent to which Congress has charged the agency with administering the criminal statute”). Accordingly, we looked at whether the agen cy’s interpretation was “a reasonable or permissible one” and was “not in conflict w ith interpretive norms regarding criminal
statutes.” Id. & n.5 (stating that “criminal statutes must be construed narrowly, and that exceptions to those statutes must be cons trued broadly”). We concluded that the agency’s interpretation was reasonable and ga ve deference to its interpretation of the “criminal provision” at issue. 7 Id. at 1287, 1291. And contrary to Mr. Aposhian’s assertion, the majority in Oklahoma Fixture did not apply, or even mention, the rule of lenity. See id. at 1287–90. We later gave deference under Chevron to a “reasonable” ATF regulation interpreting 18 U.S.C. § 922(g ), despite the “criminal nature of that statute.” United States v. Atandi , 376 F.3d 1186, 1189 (1 0th Cir. 2004) (stating that “we unquestionably owe ‘some deference’ to the ATF’s regulation”) (quoting Okla. Fixture , 332 F.3d at

7 Notably, in contrast with the regulation in Babbitt and the regulation at issue here, the NLRB’s interpretation in Oklahoma Fixture carried only criminal implications. 332 F.3d at 1291 n.1. (Briscoe, J., concurring).21 1286–87, and citing Babbitt , 515 U.S. at 703). We emphasiz ed that, as in this case, ATF “had been delegated authority to implement” § 922 by vi rtue of 18 U.S.C. § 926(a), id. (noting that § 926(a) “authoriz[es] ‘such rule s and regulations as are necessary to carry out the provisions of this ch apter’”), and we again did not invoke the rule of lenity. See id. 8 We once again gave deference under Chevron to an agency’s interpretation of a statute with criminal implications in United States v. Hubenka , 438 F.3d 1026, 1032–34 (10th Cir. 2006). In Hubenka , a jury found the defendant guilty of violating the Clean Water Act, and the defendant co ntended that “his activities . . . l[ay] beyond the reach of the [statute]” as interpreted by the Army Corps of Engineers. Id. at 1028. We nonetheless applied the Chevron framework and did not invok e the rule of lenity. Id. at 1031 (“When a case involves an agency’s inte rpretation of a statute it administers, this court uses the two-step approach announced in Chevron . . . .”). We held that the Army Corps of Engineers’ “tributary rule [was] a pe rmissible interpretation of the [statute].” Id. at 1034. Therefore, we stated that, “under Chevron , we must defer to the Corps’ interpretation of the statute” despite the criminal implications of the rule. Id. at 1034 (affirming the defendant’s convic tion). In sum, this court has repeatedly given agency interpretations with criminal law implications deference.

8 In York v. Secretary of the Treasury , 774 F.2d 417, 419 (10th Cir. 1985), we recognized ATF’s “enforcemen t power” under 26 U.S.C. § 7805(a) “to interpret 26 U.S.C. § 5845(b),” the statute at issue in th is case, “which provides that a ‘machine gun’ includes ‘any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger.’”22 To be sure, the Supreme Court has re cently “signaled some wariness about deferring to the government’s interpre tations of criminal statutes.” Guedes , 920 F.3d at 25 (citing Abramski , 573 U.S. at 191, and Apel , 571 U.S. at 369). But as the D.C. Circuit explained in Guedes , those statements “were made outside the context of a Chevron

eligible interpretation.” Id. Specifically, [i]n Abramski , the Court declined to extend deference to informal guidance document s published by [ATF]. See 573 U.S. at 191. And in Apel , the Court declined to defer to an interpretation contained in “Executive Branch documents” that were “not intended to be binding.” 571 U.S. at 368. When directly faced with the question of Chevron ’s applicability to an ag ency’s interpretation of a statute with criminal applications through a full-dress regulation , the Court adhered to Chevron

. See Babbitt , 515 U.S. at 704 n.18. Id. (emphasis added). Babbitt and our court’s precedents govern here, where ATF has promulgated a regulation through formal notic e-and-comment proceedings. Under those precedents, Mr. Aposhian has failed to demons trate a likelihood of success in establishing a rule against deference to agency interpretations with criminal law implications.
B Because the precedents cited ca ll for the application of Chevron , we now examine the Final Rule under Chevron . We first ask whether the ag ency-administered statute is ambiguous on the “precise question at issue.” Chevron , 467 U.S. at 842. If the statute’s meaning is unambiguous, then we need go no further. If we find ambiguity, our caselaw instructs us to proceed to Chevron ’s second step and ask whethe r the agency has provided a “permissible construction” of the statute. Id. at 843. There, “the task that confronts us is to decide, not whether [the agency’s inte rpretation is] the best interpretation of the23 statute, but whether it repr esents a reasonable one.” Atl. Mut. Ins. Co. v. Comm’r , 523 U.S. 382, 389 (1998). The NFA and GCA both define “machi negun” to mean “any weapon which shoots, is designed to shoot, or can be readily restored to shoot, au tomatically more than one shot, without manual reloading, by a sing le function of the trigger.” 26 U.S.C. § 5845(b); see 18 U.S.C. § 921(a)(23). The definiti on of “machinegun” also includes “any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun, an d any combination of parts from which a machinegun can be assemb led if such parts are in the possession or under the control of a person. ” 26 U.S.C. § 5845(b). The Final Rule determines that semiauto matic rifles equipped with bump stocks are “machineguns” because they “function[ ] as the result of a self-acting or selfregulating mechanism that allows the firing of multiple rounds” through “a single pull of the trigger.” Final Rule at 66,553. Applying Chevron , the statutory definition of “machinegun” is ambiguous, and ATF’s inte rpretation is reasonable. Mr. Aposhian therefore is unlikely to succeed on the mer its of his challenge to the Final Rule. (i) For the first step, to ascertain whether C ongress clearly stated its intent on the precise statutory question at issue, courts shou ld “apply[] the ordinary tools of statutory construction.” City of Arlington v. FCC , 569 U.S. 290, 296 (2013). “These tools include examination of the statute’s text, structure, purpose, history, and relationship to other
statutes.” Harbert v. Healthcare Servs. Grp., Inc. , 391 F.3d 1140, 1147 (10th Cir. 2004).24 “Ambiguity is a creature not of definitiona l possibilities but of statutory context.” Brown v. Gardner , 513 U.S. 115, 118 (1994). Under th is analysis, we agree with the D.C. Circuit that two features of the statutory de finition of “machinegun” render it ambiguous. The first is the phrase “single function of the trigger,” and the second is the word “automatically.” Guedes , 920 F.3d at 29. “Single Function of the Trigger” When applied to bump stocks, the st atutory definition of machine gun is ambiguous with respect to the phrase “single function of the tr igger.” That is because, within the statutory context, the phrase can have more than one meaning. See id. (“[T]he statutory phrase ‘single function of the trigger’ admits of more than one interpretation.”). Mr. Aposhian defines the phrase to mean a me chanical act of the trigger. Aplt. Br. at 26 (arguing that “[c]ourts have emphasized th at a trigger’s function is defined by how it mechanically operates, not by how the shoot er engages it”). The government (and ATF), however, define “single function of the trigger” as “single pull of the trigger,” Aple. Br. at 14, which “considers the external im petus for the mechanical process.” Gun Owners of
Am. v. Barr , 363 F. Supp. 3d 823, 83 2 (finding “the statutory definition of machine gun” to be “ambiguous with resp ect to the phrase ‘single function of the trigger’”). 9

9 The dissent states that ATF’s interpretati on of “single function of the trigger” to mean “single pull of the trigger” refers onl y to the action of the trigger and not the volitional action of the shooter. Dissent at 7. The parties argue othe rwise. Specifically, Mr. Aposhian and the government agree that ATF’s interpreta tion refers to the action of the shooter’s trigger finger. See Aplt. Br. at 25 (arguing that the Final Rule conflicts with the statute because it redefines “single func tion of the trigger” to mean only the “deliberate and volitional act of the user pulli ng the trigger”) (quotations omitted); Aple. Br. at 20 (arguing that the statute “is concerned with the shooter’s act of pulling the25 As the D.C. Circuit explained, The first interpretation would tend to exclude bump-stock devices: while a semiautomatic rifle outfitted with a bump stock enables a continuous, high-sp eed rate of fire, it does so by engendering a rapid bumping of the trigger against the shooter’s stationary finger, su ch that each bullet is fired because of a distinct mechani cal act of the trigger. The second interpretation would te nd to include bump-stock devices: the shooter engages in a single pull of the trigger with her trigger finger, and th at action, via the operation of the bump stock, yields a continu ous stream of fire as long she keeps her finger stationary and does not release it. Guedes , 920 F.3d at 29. Within the statutory context, the phrase could have either meaning. The word “function” focuses on the “mode of action,” 4 Oxford English Dicti onary 602 (1933), or “natural . . . action,” Webster’s New Internat ional Dictionary 876 (1933), by which the trigger operates. But that definition begs the question of whether “function” requires our focus upon the movement of the trigger, or the movement of the trigger finger. The statute is silent in this rega rd. “In light of those competi ng, available interpretations, the statute contains a ‘gap fo r the agency to fill.’” Guedes , 920 F.3d at 29 (quoting Chevron , 467 U.S. at 843). Mr. Aposhian argues that “single func tion of the trigger” plainly means a mechanical movement of the trigger, asserti ng that Congress understood when it enacted

trigger”) (emphasis added). Because the pa rties do not argue that ATF’s interpretation refers to the action of the trigger, that argument is waived. See Wyoming v. Livingston , 443 F.3d 1211, 1216 (10th Cir. 2006). We ac knowledge the parties’ agreement on this issue, not to support our conclusion that the statute is ambiguous, but rather to explain why we do not address the argument th at is the focus of the dissent.26 the NFA that there was a “difference in the internal mechan ism that allowed a machinegun to fire multiple r ounds continuously with one function of the trigger and a semiautomatic weapon, which fires only one ro und with each functi on of the trigger.” Aplt. Br. at 36. But this distinction in no way requires a “function” to be a mechanical action. In fact, the definition Congress gave to the term “semiautom atic rifle” in the GCA is “any repeating rifle which utilizes a po rtion of the energy of a firing cartridge to extract the fired cartridge case and chamber th e next round, and which requires a separate pull of the trigger to fire each cartridge.” 18 U.S.C. § 921(a)(28) (emphasis added). We conclude the statutory definition of machine gun is ambiguous with respect to the phrase “single function of the trigger.” “Automatically” Similarly, the statutory term “automatica lly” is ambiguous when applied to bump stocks. In the statute, “automatically” f unctions as an adverb modifying the verb “shoots.” Relying on definitions from the 1930s, the government and the Final Rule interpret the word to mean “the result of a self-acting or self-regulating mechanism.” Final Rule at 66,519. Mr. Aposhian counter s that because the sh ooter must maintain constant rearward pressure on the extension ledge with the trigger finger and constant forward pressure with the non-trigger hand for the bump stock to work, a bump stock cannot shoot “automatically.” Ap lt. Br. at 22–23. Essentially , “the parties’ dispute is whether the . . . pressure exerted by the sh ooter . . . requires the conclusion that a bump stock does not shoot automatically.” Gun Owners , 363 F. Supp. 3d at 831.27 The statutory text does not answer this question. The term “automatically,” however, does not require there be no human involvement to give rise to “more than one shot.” Webster’s New Intern ational Dictionary provides that “automatically” is the adverbial form of “automatic,” meaning “[ h]aving a self-acti ng or self-regulating mechanism that performs a required act at a predetermined point in an operation.” Webster’s New International Dictionary 187 (2d ed. 1934) (emphasis added); see also Webster’s New International Di ctionary 156 (1933) (defining “automatic” as “self-acting or self-regulating,” especially applied to “machinery or devices which perform parts of the work formerly or usually done by hand”) (emphasis added). Similarly, the Oxford English Dictionary defines the term to mean “[s]elf-acting under conditions fixed for it , going of itself.” 1 Oxford Eng lish Dictionary 574 (1933) (e mphasis added). Therefore, under its ordinary meaning, the term can be read to permit limited human involvement to bring about “more than one shot.” As the D.C. Circuit explained, [A] quite common feature of weapons that indisputably qualify as machine guns is that they require both a single pull of the trigger and the application of constant and continuing pressure on the trigger after it is pulled. We know, therefore, that the requirement of some measure of additional human input does not render a weapon nonautomatic. Guedes , 920 F.3d at 30 (emphasis in original ) (citation omitted). But how much human input is too much? The statute does not say. Mr. Aposhian cites Staples v. United States , 511 U.S. 600, 602 n.1 (1994), for the proposition that the shooter’s manual manipula tions of the weapon clearly do not meet the definition of “automatically.” See Aplt. Br. at 18, 21. Reliance on Staples is28 misplaced. Staples concerned the necessary mens rea element for a conviction for possession of an unregistered machine gun under the NFA. 511 U.S. at 604. At the beginning of the opinion, the Court provide d a footnote explaining how it was using certain terms in the opinion, includi ng “automatic” and “semi-automatic.” Id. at 602 n.1. It stated, [a]s used here, the terms “automatic” and “fully automatic” refer to a weapon that fires repe atedly with a single pull of the trigger. That is, once its trigger is depressed, the weapon will automatically continue to fire until its trigger is released or the ammunition is exhausted. Such weapons are “machineguns” within the meanin g of the Act. We use the term “semiautomatic” to design ate a weapon that fires only one shot with each pull of the trigger, and which requires no manual manipulation by the operator to place another round in the chamber after each round is fired. Id. (emphasis added). As the Seventh Circuit explained in United States v. Olofson , 563 F.3d 652, 657 (7th Cir. 2009), the statutory definition of these terms was not at issue in Staples , and the Court was not purporting to interpret the st atute. Instead, “the Court simply was providing a glossary for terms frequ ently appearing in the opinion.” Id. Moreover, the Court did not suggest that “automatic” firing excluded all “manual manipulation” of the gun, as Mr. Aposhian maintains. The Co urt mentioned “manual manipulation” only in connection with placing another round in the chamber. Staples , 511 U.S. at 602 n.1. Precluding “manual manipulation” to put another round in the chamber is not inconsistent with the statutory definition of a machine gun , which shoots more th an one shot “without manual reloading,” 26 U.S.C. § 5845(b).29 In sum, the statutory defi nition of machine gun contai ns two central ambiguities, both of which ATF has attempted to reso lve. Accordingly, we proceed to Chevron ’s second step. (ii) When, as here, Congress leav es an implicit statutory gap, we ask at step two “whether the [regulation] is based on a pe rmissible construction of the statute.” Chevron , 467 U.S. at 843. “‘[T]he agency’s interp retation need not be the only one it could have adopted, or the one that this court would have re ached had the question initially arisen in a judicial proceeding.’” Anderson v. Dep’t of Labor , 422 F.3d 1155, 1181 (10th Cir. 2005) (quoting Salt Lake City v. W. Area Power Admin. , 926 F.2d 974, 978 (10th Cir. 1991)). ATF’s interpretation of “single function of the trigger” to mean “single pull of the trigger” is a permissible reading of the statute. See Guedes , 920 F.3d at 31 (concluding ATF’s interpretation of “single functi on of the trigger” is permissible); Gun Owners , 363 F. Supp. 3d at 832 (same). ATF’s interpretati on accords with how some courts have read the statute. For example, in Akins , the Eleventh Circuit held that ATF’s reading of “single function of the trigger” to mean “sin gle pull of the trigger” was “consonant with the statute and its legislative history.” 312 F. App’x at 200 (concluding that the Akins Accelerator, a type of bump stock, was reas onably classified as a machine gun). In addition, the Final Rule’s interpretation “accor ds with how the phrase ‘single pull of the trigger’ was understood at the time of the enactment of the [NFA].” Guedes , 920 F.3d at
31. The Final Rule cites a congressional hearing for the NFA where the then-president of30 the National Rifle Association testified that the term “machine gun” included any firearm “capable of firing more th an one shot by a single pull of the trigger, a single function of the trigger.” Final Rule at 66,518 (emp hasis added). Further, the House Report accompanying the bill that eventually became the NFA states that the bill “contains the usual definition of a machine gun as a weapon designed to shoot more than one shot . . . by a single pull of the trigger.” H.R. Rep. No. 73-1780, at 2 (1934) (emphasis added). Nonetheless, the dissent states that if the Final Rule does refer to the motion of the trigger finger—a proposition the parties do not dispute—then the regulation is invalid as being broader than the unambiguous NFA. Dissent at 8 n.3. Th is assertion is contrary to authority in this circuit. Specifically, this court has looked to a shooter’s volitional actions to determine whether automation wa s obtained with a “single function of the trigger” under the NFA. See United States v. Oakes , 564 F.2d 384, 388 (10th Cir. 1977).

In Oakes , we held that a “gun was a machine gun within the [NFA’s] statutory definition” because “the shooter could, by fully pulling the trigger . . . obtain automation with a single trigger function .” Id. (emphasis added). Thus, ratherthan being broader than the NFA, ATF’s interpretation of “single function of the trigger” accords with how this court has interpreted the statute. ATF’s interpretation of “automatically” is likewise permissible. The Final Rule’s “definition accords with the everyday understanding of the word ‘automatic.’” Guedes , 920 F.3d at 31. That is, the bump stock “p erforms a required act at a predetermined point” in the firing sequence by directing the recoil energy into the space created by the sliding stock. The bump stock is also “sel f-acting under conditions fixed for it.” The31 shooter’s positioning of the trigger finger on the extension ledge and application of forward pressure on the front of the gun provide the conditio ns necessary for the bump stock to repeatedly perform its purpose: to e liminate the need for the shooter to manually capture the recoil energy to fire additional rounds. We therefore disagree with the dissent’s contention that a bump stock canno t be “automatic” because it will not work without constant forward pressure. Di ssent at 12. The bump stock performs part of the work usually done by hand at a predetermine d point in the operation, under conditions fixed for it by the shooter. In addition, ATF’s interpretation focuse s the inquiry about what needs to be automated precisely where the statute does: th e ability of the trigger function to produce “more than one shot, without manual reloading.” 26 U.S.C. § 5845(b); see Guedes , 920 F.3d at 31–32. Further, ATF’s interpreta tion tracks the interpre tation reached by the Seventh Circuit, where the court interpreted the term to require a “self-acting mechanism” without requiring more. Olofson , 563 F.3d at 658; see also Guedes , 920 F.3d at 32; Gun Owners , 363 F. Supp. 3d at 832 (holding that ATF’s “interpretation [of the term ‘automatically’] is consistent with judicial interpretations of the statute”). Because ATF’s Final Rule sets forth a r easonable interpretation of the statute’s ambiguous definition of “machi negun,” it merits our deferenc e. Mr. Aposhian has not demonstrated a likelihood of success on the me rits of his challenge to the Final Rule. IV Although we could affirm the district court’s denial of preliminary injunctive relief solely on the ground that Mr. Aposhian has failed to demonstrate a substantial32 likelihood of success on the mer its, we also conclude that Mr. Aposhian has not met the other prerequisites for preliminary relief. Irreparable Harm At the district court, “[t]he parties [did] not dispute that Mr. Aposhian will experience irreparable harm if the injunction is denied.” Aplt. App. at 175. They did “disagree about what that irreparable harm is.” Id. at n.4. Mr. Aposhian argued only that he would “be harmed by being forced to comply with a rule that has been promulgated in contravention of constitu tional principles of se paration-of-powers.” Id. The government conceded only that th e irreparable harm was the loss of Mr. Aposhian’s bump stock. Id. On appeal, Mr. Aposhian ag ain contends that he will suffer irreparable harm because the Final Rule was i ssued in violation of his constitutional rights—specifically, the separation of powers doctrine. Aplt. Br. at 48. The government now asserts that Mr. Aposhian will not suffer irreparable harm, contending that there is no support for the proposition that a generalized separation-of -powers violation constitutes irreparable harm. Aple. Br. at 44. We agree with the government that Mr. Aposhian has not met his burden of demonstrati ng irreparable harm. Mr. Aposhian relies on our holding in Free the Nipple-Fort Collins v. City of Fort Collins , 916 F.3d 792, 806 (10th Cir. 2019), where we held that “[w]hat makes an injury ‘irreparable’ is the inadequacy of, and the difficulty of calculating, a monetary remedy after a full trial.” We noted that “[a]ny deprivation of any constitutional right fits that bill.” Id. But in the merits portion of his openi ng brief, Mr. Aposhian does not cite to a single constitutional provision or rely on any c onstitutional theory to argue that the Final33 Rule is invalid; rather, his arguments focus on whether the Final Rule contradicts the

statute. 10 We cannot conclude that Mr. Aposhi an has shown irreparable harm based on the deprivation of a constitutional right when he does not even raise a constitutional challenge to the Final Rule in this court. Even if Mr. Aposhian had properly raised a constitutional argument, he has not cited a single case where a generalized se paration of powers, by itself, constituted irreparable harm. To the contrary, our cases finding that a violation of a constitutional right alone constitutes irreparable harm are limited to cases involving individual rights, not the allocation of powers amo ng the branches of government. See, e.g. , Free the Nipple , 916 F.3d at 806 (alleged equal protection violation); Awad v. Ziriax , 670 F.3d 1111, 1119 (10th Cir. 2012) (allege d First Amendment violation); see generally 11A Charles Alan Wright, Arthur R. Miller & Mary Kay Kane, F ED

. P RAC

. & P ROC

. § 2948.1 (3d ed. 2019) (“When an alleged deprivation of a constitutional right is involved, such as the right to free speech or freedom of religion , most courts hold that no further showing of irreparable harm is necessary.”) (emphasi s added). For these reasons, he has not met his burden of demonstrating that he would suffer irreparable harm absent an injunction. The dissent asserts that the government ha s waived any argument as to irreparable harm by conceding in the district court that Mr. Aposhian would suff er irreparable harm. Our precedent says otherwis e. For instance, in Dominion , the parties stipulated in a contract that a breach of an ex clusivity provision wo uld give rise to irreparable harm and

10 As noted, the constitutional arguments Mr. Aposhian raised fo r the first time in a footnote in his reply brief are waived. Sylvia , 875 F.3d at 1332 n.7.34 warrant injunctive relief. 356 F.3d at 1261. The district court relied solely on the parties’ stipulation to find that the plaintiff had met its burden of demonstra ting irreparable harm. Id. at 1266. We reversed, concluding that the “stipulation without more is insufficient to support an irreparable harm finding.” Id. The same holds true here. We emphasize that it is Mr. Aposhian’s burden to demonstrate irreparable harm. Awad , 670 F.3d at 1128 n.14 (noting that the pl aintiff has the “burden under [each of] the four preliminary injunction factors”). While th e government stated in the district court that the loss of Mr. Aposhian’s bump stoc k would constitute i rreparable harm, Mr. Aposhian has never made a loss-of-property ar gument. Therefore, he has waived this argument and cannot rely on it to satisfy his burden. 11
Harm to the Government and the Public Interest Mr. Aposhian has also failed to meet th e remaining prerequisites for a preliminary injunction. Specifically, he has not shown that the threatened injury outweighs the harms that the preliminary injunction will cause the government or th at the injunction, if issued, will not adversely affect the public interest. These factors “merge” when the government is the opposing party. Nken , 556 U.S. at 435. Mr. Aposhian argues that the “balance of equities” favors an injunction, stating that the public interest weighs in his favor because the public has an interest in protecting

11 In any event, we note that the loss of a bump stock cannot constitute irreparable harm because Mr. Aposhian could be awarded compensatory damages. See Salt Lake Tribune Pub. Co., LLC v. AT&T Corp. , 320 F.3d 1081, 1105 (10th Cir. 2003) (“Irreparable harm, as the name suggests, is harm that cannot be undone, such as by an award of compensatory damages or otherwise.”).35 an individual’s constitutional rights. Aplt. Br. at 49–50. But Mr. Aposhian has not argued that the Final Rule violates an individual constitutional right. Moreover, the public has a strong interest in banning th e possession and transfer of machine guns, including bump stocks. The ban supports the safety of the public in general, see Final Rule at 66,515, and the safety of law enforcement officers and first responders, id. at 66,551. Mr. Aposhian counters that because he is a law-abiding citizen, “ATF cannot plausibly suggest that public safety demand s that he be deprived of his device any longer.” Aplt. Br. at 50. The government’s general public safety concerns, however, still apply to Mr. Aposhian. Congress has prohib ited Mr. Aposhian, no less than any other individual, from owning a bump stock. See Gun Owners , 363 F. Supp. 3d at 834 (“Congress restricts access to machine guns b ecause of the threat the weapons pose to public safety . . . All of the public is at risk, including the smaller number of bump stock owners.”). We conclude, and the dissent does not disagree, that Mr . Aposhian has failed to demonstrate that the threat ened injury to him outweighs the harm th at the preliminary injunction may cause to the gov ernment or that the injunction will not adversely affect the public interest. V For the foregoing reasons, we affirm the district court’s denial of a preliminary injunction.Aposhian v. Barr, et al. , 19-4036 CARSON, J., dissenting. In our Republic, Congress has the power to make and change laws. U.S. Const. art. I. Yet that preferred route often takes a ba ck seat to a more expedient one. As is now often the case, the Executive Br anch steps in and seeks to re medy an unpopular or poorly drafted law through an administ rative regulation. And to be sure, the Execut ive can do so when the law is ambiguous; the Supreme Co urt has made as much clear. Chevron, U.S.A., Inc. v. Nat. Res. Def. Co unsel, 467 U.S. 837 (1984). But regardless of the Executive’s ability to repair ambiguous laws, unambiguous laws—no matter how problematic or out of favor—are out of its reach. See Epic Sys. Corp. v. Lewis, 138 S. Ct. 1612, 1630 (2018) (explaining that Chevron deference is unwarranted when “traditional tool[s] of stat utory construction” ar e “up to the job of solving [a statute’s] interpretive puzzle”); Bi g Horn Coal Co. v. Sadler, 924 F.3d 1317, 1322 (10th Cir. 2019) (“[I]f Congress has spoken ‘directly’ to the ‘precise question at issue,’ the inquiry ends, and we must give effect to the express intent of Congress.” (quoting Chevron, 476 U.S. at 842)). Thus, when a party challenges a regulation that implements an unambiguous law in court, the Judiciary must be mindful that neither it nor the Executive has the power to make the law. See Sessions v. Dimaya, 138 S. Ct. 1204, 1228 (2018) (Gorsuch, J ., concurring). Rather, those two branches “must respect the role of the Legislature, and take care not to undo what it has done.” King v. Burwell, 135 S. Ct. 2480, 2496 (2015). In short, Congress must fix a ny flaw that may exist in a2 particular piece of unambiguous legislation; the Executive and the Judiciary may not do so no matter how tempting the fix may be. Today we encounter an example of unamb iguous legislation that neither the Executive nor the Judiciary may cast asunde r: the National Firearms Act (NFA), 26 U.S.C. §§ 5801–72. As the ma jority notes, that law regul ates “machinegun[s],” which comprise “any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger.” 26 U.S.C. § 5845(b). That clear language leaves little wiggle room. The word “automatically,” fo r instance, takes on its usual definition and refers to mechanisms that are “self-acting or self-regulating” rather than mech anisms that are not self-acting or self-regulating. And the phrase “single func tion of the trigger” speaks only about the trigger itself; the phrase mentions nothing about the external stimulus that interacts with the trigger. Thus, to qualify as a machine gu n under the NFA, a firearm must satisfy at least two conditions: (1) the trigger itself must “function” only once to fire more than one shot, and (2) the mechanism that allows the triggerto “function” only once must be “selfacting or self-regulating.” As I explain below, a semiautomatic firear m equipped with a bump stock satisfies neither of those conditions. For one thing, the trigger on such a firearm must still “function” every time a shot is fired. And in any event, the bump stock—at least the nonmechanical variety—is not “self-acting or self-regulating” on the trigger. Why? Because the user of the firearm must also apply constant forward pressure with his or her3 nontrigger hand for the bump stock to work. 1 So does a bump st ock increase the speed by which the user can fire rounds? Yes. Bu t does that mean the firearm to which it is attached is a machine gun under th e NFA? No. Yet the Bureau of Alcohol, Tobacco, Fire arms, and Explosives (ATF) now thinks so. In the wake of the tragic Las Vegas sh ooting, ATF promulgated a final administrative rule in late 2018 that classifies “bump-st ock-type devices” as “machinegun[s]” under the NFA. See Bump-Stock-Type Devices, 83 Fed. Reg. 66,514 (Dec. 26, 2018) (the BumpStock Rule). ATF declared th at a machine gun includes a device that allows a semiautomatic fi rearm to shoot more than one shot with a single pull of the trigger by harnessing the recoil energy of the semiautomatic firearm to which it is a ffixed so that the trigger resets and continues firing without additional phys ical manipulation of the trigger by the shooter. Id. at 66,553–54. That rule cannot withstand judicial scru tiny. As applied, the Bump-Stock Rule focuses on the user’s trigger fi nger instead of the trigger itself, which flouts the phrase “single function of the trigger ” in the NFA. 26 U.S.C. § 5 845(b) (emphasis added). The Bump-Stock Rule also fails to consider that the user must apply constant forward pressure with his or her nontrigger hand (a ta sk that requires a fair amount of strength and dexterity) to make the bump stock work, which runs afoul of the word “automatically” in the NFA. Our inquiry should begin and end with that strai ghtforward statutory analysis.

1 Mechanical bump stocks use slightly different mechanisms. The Akins Accelerator, for instance, uses internal springs instead of c onstant forward pressure to propel the firearm forward.4 I therefore must respectfully dissent from the majority’s conclusion that the NFA’s definition of a machine gun is ambiguous as applied to bump stocks and that we must uphold the Bump-S tock Rule through Chevron deference. Neither the Judiciary nor the Executive has the power to make or change law by creating an ambiguity where none exists. To do so (as both ATF did and th e majority does today) subverts the constitutional prerogatives of each branch of government. To be clear: I express no opinion on wh ether the Second Amendment protects bump stocks, nor do I express an opinion ab out whether any American citizen even has a valid reason to own a bump stock. Neither of those inquiries is before us today, and I do not base my dissent on any personal convicti ons about how a court sh ould answer them. Rather, I dissent simply because the unambigu ous language of the NFA establishes that Plaintiff W. Clark Aposhian is likely to suc ceed on the merits of his challenge to the Bump-Stock Rule. And in any even t, even if the NFA’s language were ambiguous, I cannot endorse the majority’s decision to uphold the Bump-S tock Rule th rough Chevron deference. Applying Chevron is misguided for two distinct reasons : ATF disavowed that doctrine in its briefing, and th e definition of “machinegun” in the NFA carries criminal consequences. Finally, ATF wa ived its argument that Plaintiff will not suffer any irreparable harm, which simply bolsters th e conclusion that Plaintiff is entitled to preliminary injunctive relief. 2

2 The majority relies on the reasoning in th e D.C. Circuit’s opinion in Guedes v. Bureau of Alcohol, Tobacco, Firearms & Explosives, 920 F. 3d 1 (D.C. Cir. 2019), cert. denied, 140 S. Ct. 789 (2020). I agree w ith Judge Henderson’s thoughtful and wellcrafted partial dissent in that case.5 I. Consider again how a nonmechanical bump stock operates. The bump stock replaces the standard stock of a rifle—the part of the gun that rests against a shooter’s shoulder. A shooter pulls the trigger. The kickback or re coil causes the gun to slide backward. The shooter keeps his or her trig ger finger stationary, maintaining backward pressure on the trigger. At the same time, the shooter must also apply forward pressure with his or her non-shooting ha nd. This process of forward pressure with one hand and backward pressure with the other causes the firearm to slide back and forth rapidly, which bumps the stationary fi nger against the moving tri gger. The result: the trigger resets rapidly, which causes the rifle to fire many shots over a short time. Bump-Stock Type Devices, 83 Fed. Reg. at 66,516. ATF believes that process transforms a fi rearm into a weapon that shoots more than one shot “automatically . . . by a si ngle function of the trigger.” 26 U.S.C. § 5845(b). To get there, ATF first clarifie d in the Bump-Stock Rule that the word “automatically” means “functioning as the re sult of a self-acting or self-regulating mechanism that allows the firing of multip le rounds through a single function of the trigger.” Bump-Stock-Type Devices, 83 Fed. Reg. at 66,553; see also 27 C.F.R. § 447.11. It next clarified that the phrase “single function of the trigger” means “single pull of the trigger and analogous motions.” Bump-Stock-Type Devices, 83 Fed. Reg. at 66,553; see also 27 C.F.R. § 447.11. And it finally concluded that those clarifying definitions cover bump stocks:6 [W]hen a shooter who has affixed a bump-stock-type device to a semiautomatic firearm pulls the tri gger, that movement initiates a firing sequence that produces more than one shot. And that firing sequence is “automatic” because the device harnesses th e firearm’s recoil energy in a continuous back-and-forth cycle that a llows the shooter to attain continuous firing after a single pull of the trigger , so long as the trigger finger remains stationary on the device’s ledge (as designed). Bump-Stock-Type Devices, 83 Fed. Reg. at 66,519 (emphases added). I take no issue with ATF’s definitions that clarify the meanings of “automatically” and “single function of the trigge r.” But as I explain below, applying those definitions to nonmechanical bump stocks cannot lead to ATF’s pref erred result. I discuss each in turn.
A. I begin with the phrase “si ngle function of the trigger.” As mentioned, the BumpStock Rule defines that phras e to mean “a single pull of the trigger and analogous motions.” 27 C.F.R. § 447.11 . When one dissects that la nguage, the reason it cannot apply to bump stocks becomes apparent. To start, I agree with the majority th at the word “function” means “action.” Webster’s New International Dic tionary 876 (1933). That much is clear. But I part ways with the majority when it conc ludes that the “statute is silent” (and therefore ambiguous) as to whether that action centers on “the move ment of the trigger, or the movement of the trigger finger.” In fact, the statute speaks clearly: the func tion/action must be “of the trigger.” The NFA mentions nothing about trigger finger or any other “external impetus” that happens to interact with the trigger. Guedes v. Bur. of Alcohol, Tobacco, Firearms & Explosives, 920 F.3d 1, 43 (D.C. Cir. 2019) (Henderson, J ., concurring in part and dissenting in part)7 (observing that the word “function” in the NFA “focus[es] on how the trigger acts”). And given that omission, we must presume “tha t [the] legislature says . . . what it means and means . . . what it says”—that is, we mu st presume that the function/action of the trigger itself is the only variable that matters . Henson v. Santande r Consumer USA Inc., 137 S. Ct. 1718, 1725 (2017) (alterations in original) (quoting Dodd v. United States, 545 U.S. 353, 357 (2005)). By concluding otherwis e and allowing an inqu iry into the trigger finger , the majority effectively “replac[es] th e actual text” of the NFA “with speculation as to Congress’ intent.” Magwood v. Patte rson, 561 U.S. 320, 3 34 (2010). That the majority cannot do without taki ng on a legislative role. As a result, Congress’s use of the phrase “single function of the trigger” in the NFA can mean only “single action of the trigger” and not “single action of the trigger finger.” The clear language ties our hands. Necessarily, then, ATF’s interpretation of the phrase “single function of the trigger”—i.e., “single pull of the tri gger and analogous motions”—can refer only to the action of the trigger and not the trigger finger. See Guedes, 920 F.3d at 43 (D.C. Cir. 2019) (Henderson, J., concurring in part and dissenting in part) (“[N]othing in the [Bump-Stock] Rule’s definition refers to a shooter’s finger or a volitional action.”). That is the only way for ATF’s interp retation to remain valid. Otherwise, ATF’s interpretation would contradict the unambiguous NFA—the interpretation would refer to the trigger finger, while the statute refers to the trigger alone—and “[a] regulation in conflict with8 the terms of an unambiguous st atute will not be sustained.” Burnet v. Marston, 57 F.2d 611, 612 (D.C. Cir. 1932). 3 That limitation on the phrase “single pull of the trigger and analogous motions” sounds the death knell for ATF’ s new take on bump stocks. For as I alluded to above, a semiautomatic rifle equipped w ith a bump stock simply does not use a single function of the trigger to fire more than one shot. To illustrate, first consider the basic mech anics of a semiautomatic rifle that lacks a bump stock. The trigger on that type of rifle must necessarily “pull” backwards and release the rifle’s hammer—the part of a rifle that sets in motion ho w the bullet leaves the barrel—every time that the rifle discharges. See Plaintiff-Appellant’s App’x A73–A74. The rifle cannot fire a second round until both th e trigger and hammer reset. Only then can the trigger “pull” backwards once more and reinitiate the entir e firing process from the beginning. A bump stock cannot change that process. The trigger on a semiautomatic rifle equipped with a bump st ock still pulls backwards every time that the rifle fi res. The only difference is that recoil—not the operator’s finger—causes that pull. See Guedes, 920

3 The majority points out that the parties agree that ATF’s interpretation refers to the action of the shooter’s trigger finger. Bu t that agreement does no t help the majority in any way. Again, if the regulation does refer to the motion of the trigger finger, the regulation is invalid because it conflicts with the unambiguous NFA. Burnet, 57 F.2d at 612 (“While the [agency] was clothed with au thority to promulgate regulations, [it] was not authorized to add to or take from the pl ain language of the statute, for, ‘where the intent is plain, nothing is leftto construction.’” (quoting Unite d States v. Fisher, 6 U.S. (2 Cranch) 358, 386 (1805)). I simply choose to give the regulation the benefit of the doubt.9 F.3d at 48 (Henderson, J., concurring in part and dissenting in part) (“A semiautomatic rifle shoots a single round per pull of the trigger and the bump stock changes only how the pull is accomplished.” (emphasis in original )). Again, the NFA demands that we look only to how the trigger acts. And given that the trigger functions every time a semiautomatic rifle equipped with a bump stock fires a ro und, such a rifle unambiguously cannot be a machine gun under the NFA even if the operator’s trigger finger remains stationary. Contrasting a bump-stock-equipped rifle w ith the machine gun that the majority references from our decision in United States v. Oakes, 564 F.2d 384 (10th Cir. 1977), reinforces my point. The gun in Oakes contained two “proj ections” in the area that a traditional trigger usually occupies. Id. at 388. The first was a “forward” projection “curved so as to fit the finger in a norma l fashion”—in other wo rds, it looked like and functioned as a regular trigger. Id. Th e second projection was “seated behind” the forward one and “curved in a ma nner so that at its extremity it would be pushed if the [shooter fully pulled the forward projection] to contact.” Id. In sum, when the shooter fully pulled the first projection/trigger, th e second projection activated and “fully automated the gun.” Id. The question in Oakes was whether that interplay between the two projections allowed the gun to fire more than one shot “by a single function of the trigger”; the government argued it did, wh ile the gun owner argued that the gun’s “two triggers” meant it did not. Id. at 387 n.2, 388. Cont ra the majority’s sugges tion today, the ultimate answer to that question did not hinge on the shooter’s voliti onal actions in any way.10 Indeed, the holding of Oakes that the weapon fit the bill of a machine gun under the NFA boiled down to the fact that “fully pulling the trigger”—t hat is, the forward projection— allowed the gun to automatically fire rounds. Id. at 388. That rationale endures even if one focuses on the shooter’s trigger finger or the trigger itself: both the finger and the trigger on such a gun “pulled” just once to fire more than one round even though a second, posterior projection fa ctored into the weapon’s auto matic mechanism. See id. We should thus draw little guidance from the la nguage in Oakes that speaks in terms of the shooter’s actions rather than the trigge r’s actions. The distinction between the two concepts made no difference to the holding, so that specific language in Oakes is no more than imprecise dicta. Toko ph v. United States, 774 F.3d 1300, 1303 (10th Cir. 2014) (“[A] panel of this court is bound by a holding of a prior panel of this court but is not bound by a prior panel’s dicta. ” (alteration and emphasis in original) (quoting Bates v. Dep’t of Corr., 81 F.3d 1008, 1011 (10th Cir. 1996))). Viewed under that lens, Oakes supports my position. That case tracks the text of the NFA: it does not defy the congressional de termination that the trigger itself must function just once to fire more than one shot. As I explain above, however, a rifle equipped with a bump stock does not fit that rubric. That type of rifle continues to use multiple functions of the trigger itself even though the shooter must take only a single volitional action. A bump stock, in other words, changes only how a trigger pulls; it does not change the fact that the trigger itself must function every shot. Under the unambiguous language of the NFA, that mean s that a bump stock cannot transform a semiautomatic rifle into a machine gun.11 B. The word “automatica lly” in the NFA unearths an ev en-more-obvious flaw in the ATF’s bump-stock ban. As a reminder, I take no issue with the ATF’s interpretation of that word—i.e., “functioning as the result of a self-acting or self-regulating mechanism that allows the firing of multiple rounds through a single functi on of the trigger.” 27 C.F.R. § 447.11. That interpretation “reflects the ordinary mean ing of that term at the time of the NFA’s enactment in 1934,” and that same ordinary me aning continues to this day. Bump-StockType Devices, 83 Fed Reg. at 66,519; see also Webster’s Ne w International Dictionary 187 (2d ed. 1934) (defining “automatic” as “[ h]aving a self-acting or self-regulating mechanism that performs a required act at a predetermined point in an operation”); Automatic, Merriam-Webster.com Di ctionary, https://www.merriamwebster.com/dictionary/automatic (last visite d Mar. 30, 2020) (defining “automatic” as “having a self-acting or self-re gulating mechanism”). The problem is again one of application. A nonmechanical bump stock is not a “self-acting or self-regulating me chanism”; the constant forwar d pressure that the shooter must apply with his or her nontri gger hand prevents that label. 4

4 In her dissent, Judge Henderson does question the ATF’s actual interpretation of the word “automatically.” See Guedes, 920 F. 3d at 42 (Henderson, J., concurring in part and dissenting in part) (“Although the [Bump-Stoc k] Rule . . . correctly interprets ‘single function of the trigger,’ it misreads ‘automatica lly.’”). But her reasons for that belief also stem from the constant forwar d pressure that the shooter must apply with his or her nontrigger hand. Id. at 43–45. Thus, no matt er if the interpretation or application of the word “automatically” is the ultimate problem , the important point is that the “extra”12 In coming to this conclusion, I do no more and no less than take the words “selfacting” and “self-regulating” at face value. If a mechanism is self-acting, it acts by itself. If it is self-regulating, it regul ates itself. A nonmechanical bump stock does neither. By design, that type of bump stock requires manual human input—constant forward pressure with the nontrigger hand—to act. And it requires that same manual human input to regulate its actions. Without the constant fo rward pressure, a nonmechanical bump stock simply will not work; the firear m to which it is attached will fire only one shot even with the stationary trigger finger applying consta nt backward pressure. A nonmechanical bump stock is therefore not “ self -acting” or “ self -regulating.” That straightforward logic also highli ghts the flaws underlying the majority’s attempt at fashioning an ambi guity from the word “automatic ally.” Again, the terms “self-acting” and “self-regulating” are self-explanatory—they exclude any manual human involvement by their very defin itions. So the majority is si mply wrong when it says that the NFA is ambiguous by failing to delineate the precise amount of necessary human input. The ordinary, dicti onary definition of “automatica lly” makes the answer clear:

none. The D.C. Circuit tried to make the majority ’s exact point by example. It observed, for instance, that even auto matic weapons “require both a single pull of the trigger and the application of constant a nd continuing pressure on the trigger after it is pulled.” Guedes, 920 F.3d at 30 (majority opinion) (emp hasis in original). It also analogized an

physical input from the nontrigger hand pr events us from classi fying nonmechanical bump-stock-type devices as machine guns.13 automatic firearm to an automatic sewing machin e that “requires the user to press a pedal and direct the fabric.” Id. (emphasis in original). Because these automatic devices require some human interaction, the D.C. Circuit posited that the word “automatically” remains ambiguous as to the precise amou nt of human input that word permits. But examples such as these only prove my ultimate point. Unlike a nonmechanical bump stock, the human involvem ent in a fully automa tic firearm and an automatic sewing machine is not a part of their mechanisms themselves . Instead, the involvement is in some way ex trinsic to their actual mechan isms. And that makes all the difference, because the terms “self-acting” and “self-regulating” only modify the word “mechanism.” See 27 C.F.R. § 447.11 (“ [T]he term ‘automatically’ . . . means functioning as the result of a self-acting or self-regulating mechanism . . . .” (emphasis added)). The continued pressure on the trigger of an automatic firearm, for example, is not part of the internal m echanism that keeps feeding cartridges into and ejecting cartridges out of the firearm’s chamber at a rapid pace. The constant pedal-pressure on an automatic sewing machine is the same way: although that pressure keeps the automatic process going, the pressure is not its elf part of the engineered mechanism that forces the needle to bob up and down. Dire cting the fabric throu gh an automatic sewing machine is an even clearer ex ample, because even if the sewer stops feeding fabric, the automatic mechanism can continue to operate. By contrast, nonmechanical bump stocks require manual human involvement at all times as part of their underlying mechanisms. As I’ve previously explained, these types of bump stocks increase a user’s firing ra te through recoil. And recoil is impossible14 without constant forward pressure from the us er’s nontrigger hand. The former hinges on the latter: no manual human input, no recoil. In other words, manual human input is a necessary element of a nonmechanical bump stock’s actual mechanism, which separates this type of bump stock from the exampl es that the D.C. Circuit put forth. For all of these reasons, a nonmechanical bu mp stock is not a “self-acting or selfregulating mechanism.” And because it is not self-acting or self-regulating, the firearm to which it is attached is unambiguously not one that shoots “automatically.”
C. In sum, both the word “automatically ” and the phrase “single function of the trigger” in the NFA are unambiguous as applie d to nonmechanical bump stocks. Plaintiff is thus likely to succeed on the merits of his challenge to th e Bump-Stock Rule.
II. Because the NFA’s terms are unambiguous, the majority inappropriately applied Chevron deference to th e Bump-Stock Rule. Bu t even if that statut e were ambiguous, at least two other reasons counsel against applying Chevron. First, the government explicitly disavowed any reliance on Chevron. That alone should have prevented the majority from applying the controversial doctrine. As Justice Gorsuch recently observed in another case about the Bump-Sto ck Rule, “[i]f the justification for Chevron is that ‘policy c hoices’ should be left to executive branch officials ‘directly accountable to the people ,’ then courts must equally respect the Executive’s decision not to make policy choices in the interpretation of Congress’s handiwork.” Guedes v. Bureau of Alcohol, Tobacco, Firear ms & Explosives, 140 S. Ct.15 789, 790 (2020) (statement of Gorsuch, J., respecting denial of certiorari) (emphasis in original) (quoting Epic Sys. Corp., 138 S. Ct. at 1630). By doing the exact opposite— that is, turning a blind eye to the govern ment’s request and ap plying Chevron anyway— the majority “place[s] an unin vited thumb on the scale in favor of the government.” Id. (statement of Gorsuch, J., resp ecting denial of certiorari). That concerns me, especially given that both the Supreme Court and our Circ uit have “often declined to apply Chevron deference when the government fails to invoke it” or otherwise rely on it. Id. (statement of Gorsuch, J., respecting denial of certiorari ); see also, e.g., Hays Med. Ctr. v. Azar, — F.3d —, No. 17-3232, 2020 WL 1922595, at *13 n.18 (10th Cir. Apr. 21, 2020); Hydro Res., Inc. v. EPA, 608 F.3d 1131, 1146 (10th Cir. 2010). If any of our precedent holds otherwise, see, e.g., TransAm Trucking, Inc. v. Admin. Re view Bd., 833 F.3d 1206, 1212 n.4 (10th Cir. 2016), perhaps the day w ill soon come when the Supreme Court definitively overrules it. Second, because the definition of “m achinegun” in the NFA “carries the possibility of criminal sanctions,” Chevron is likewise inapplicable. Guedes, 140 S. Ct. at 790 (statement of Gorsuch, J., respecting denial of certiorari); see also 18 U.S.C. § 922(o)(1) (“[I]t shall be unlawf ul for any person to transfer or possess a machinegun.”); 18 U.S.C. § 921(a)(23) (“The term ‘machinegun’ has the me aning given such term in section 5845(b) of the National Firearms Act.”). I need not belabor the point; many other jurists have written about this concern in great detail. See, e.g., Guedes, 140 S. Ct. at 790 (statement of Gorsuch, J., re specting denial of certiorari); Guedes, 920 F.3d at 39–42 (Henderson, J., concurring in part and dissenting in part); Gutierrez-Brizuela v. Lynch,16 834 F.3d 1142, 1155–57 (10th Cir. 2016) (Gorsu ch, J., concurring); Esquivel-Quintana v. Lynch, 810 F.3d 1019, 1027–32 (6th Cir. 2016) (Sutton, J., concurring in part and dissenting in part), rev’d on other grounds sub nom. Esquivel-Quintana v. Sessions, 137 S. Ct. 1562 (2017). Suffice to say that wh en, as here, a law carries both civil and criminal consequences, applyi ng Chevron can lead to troub ling and unintended outcomes. After all, “[b]ecause a single law should ha ve a single meaning, the ‘lowest common denominator’—including all rules applicable to the interpretation of criminal laws— governs all of its applications.” Esquivel- Quintana, 810 F.3d at 1028 (Sutton, J., concurring in part and dissenting in part) (q uoting Clark v. Martinez , 543 U.S. 371, 380 (2005)). That approach is the only way to ensure that the la w takes on “the least libertyinfringing interpretation.” Id. Thus, since “[ t]he Supreme Court has expressly instructed

us not to apply Chevron deference when an agency seeks to interpret a criminal statute,” Gutierrez-Brizuela, 834 F.3d at 1155 (Gorsuch, J., concurring) (emphasis in original), the logical result is that we must also not ap ply Chevron when a statute has both civil and criminal applications. With that said, the majority correctly observes that, more than once, we have given at least some deference to an agency ’s interpretation of a st atute carrying criminal repercussions. See, e.g., United States v. Hubenka, 438 F.3d 1026, 1032–34 (10th Cir. 2006); United States v. Atandi, 376 F.3d 1186, 1189 (10th Cir. 2004); NLRB v. Okla. Fixture Co., 332 F.3d 1284, 1287 (10th Cir. 2003) (en banc). And despite the Supreme Court’s recent guidance condemni ng Chevron in the cr iminal sphere, some courts (like the majority today) believe that the Supreme Co urt’s language in an earlier case muddies the17 waters. Compare Abramski v. United States, 573 U.S. 169, 191 (201 4) (“[C]riminal laws are for courts, not for the Government, to cons true.”), and United States v. Apel, 571 U.S. 359, 369 (2014) (“[W]e have never held that the Government ’s reading of a criminal statute is entitled to any deference.”), with Babbitt v. Sweet Home Chapter of Cmties. for a Great Or., 515 U.S. 687, 703–04 & n.18 (1995) (“[W]e owe some degree of deference to [the agency’s] reasonable interpretation” of a “statute [that] includes criminal penalties.”). See also Guedes, 920 F.3d at 25 (majority opini on) (drawing fine lines between Abramski, Apel, and Babbitt to give Chevron a foot hold when a statute carrying criminal repercussions is at play). Against this backdrop, my ho pe is that the Supreme Cour t will one day take up this issue to give us clear guidance for future case s. Whatever the benefits of Chevron are, none come to mind by forcing courts to expand the doctrine to statutes that bring about dual civil and criminal consequences.
III. As a final point, I disagree with the major ity’s conclusion that Plaintiff has not met his burden of proving that he would suffer irre parable harm absent an injunction. My reason is simple: the government conceded outr ight in the district court that Plaintiff would suffer irreparable harm by complyi ng with the regulation. When a party intentionally relinquishes or ab andons a theory in the distri ct court, “we usually deem it waived and refuse to considerit” on appeal. Richison v. Ernest Group, Inc., 634 F.3d 1123, 1127 (10th Cir. 2011). We should follow that rule; hold the government to its18 intentional waiver; and conclude that Plain tiff, given that waiver, has met his burden of establishing irreparable harm. The majority retorts that our decision in Dominion Video Satellite, Inc. v. EchoStar Satellite Corp., 356 F. 3d 1256 (10th Cir. 2004), forb ids that conclusion. The majority is mistaken. True enough, we he ld in Dominion that a party moving for a preliminary injunction could not establish irreparable harm simply by invoking a contractual stipulation to that fact. Id. at 1261, 1266. Even so, the opposing party in Dominion had argued in the district court that the question of irreparable harm should not hinge on the contractual stipulation alone. See, e.g., id. at 1261 (observing that the district court, “[i]n making its irreparable harm determination,” rejected some of the moving party’s arguments “[b]ased on eviden ce presented by” the opposing party); id. (noting the district court’s belief that the op posing party’s expert witnesses “persuasively demonstrated” the moving party would suffer a quantifiable loss). And therein lies the pivotal difference between Dominion in our case today: the opposing party in Dominion never intentionally waived its position on irre parable harm in court, while the opposing party in our case (ATF) did waive its position in court. A prelitigation stipulation that a party later challenges once the conflict comes to a head is far different than conceding an element of a claim to a judge. In short, th e majority compares apples and oranges. At bottom, the majority’s position means that a party w ith the burden of proof cannot overcome its burden by pointing out that the opposing party conceded an element of the claim in court. As one would expe ct, that alarming consequence skirts circuit precedent. See, e.g., Johnso n v. Spencer, 950 F.3d 680, 708 (10th Cir. 2 020) (concluding19 that defendants who had relied on claim precl usion as a defense met their burden of proof on two of the three requisite elements becau se the opposing party “concede[d] . . . the second and third elements”); Un ited States v. Sinks, 473 F.3d 1315, 1321 (10th Cir. 2007) (observing that the government can conc ede elements of the plain error standard of review, which a criminal defendant has the burd en of proof to establish). And given that precedent (and, for that matter, common judicial practice), the fact that Plaintiff and ATF had different views in the district court about the type of irreparable harm at issue is irrelevant. Because ATF conceded po int blank that Plaintiff would suffer some irreparable harm—one of the four elements of any preliminary injunction—Plaintiff’s failure to correctly identify the exact parame ters of that harm has no legal effect. 5 The majority thus fails to posit a defe nsible reason for rewarding ATF’s aboutface on appeal. And I myself cannot think of any good reason to do so when strong counterarguments—for example, that bump stoc ks are unique pieces of property, that the Bump-Stock Rule can lead to criminal consequences, and so on—suggest that ATF would (or at least should) lose on the irreparable-harm element in any event. I would

5 The same logic applies to the majority’s argument thata court’s ability to award Plaintiff compensatory damages for his bu mp stock precludes his harm from being irreparable. Even if the majority is co rrect—and I am not convin ced it is, especially given that ATF has argued in at least one othe r case that bump stock owners are ineligible for compensation, Lane v. United States, No. 3:19-CV-01492-X, 2020 WL 1513470, at *1 (N.D. Tex. Mar. 30, 2020)—that nuance make s no difference today. Again, because ATF conceded irreparable harm, Plaintiff’s purported ability to re ceive compensatory damages does not matter.20 therefore hold ATF to its in tentional waiver and conclude that Plaintiff will suffer irreparable harm from the Bump-Stock Rule. 6

IV. For all these reasons, I would reverse the di strict court’s denial of a preliminary injunction. I respectfully dissent.

6 Absent waiver, I agree thatPlaintiff cannot use our holding in Free the NippleFort Collins v. City of Fort Collins, 916 F.3d 792 (10th Cir. 2019), that “[a]ny deprivation of any constitutional right” amounts to irreparable harm. Id. at 806. Plaintiff makes no constitutional arguments today (h e only makes statutory and administrative arguments), so the language from Free the Nippl e goes nowhere from the start. With that said, in an appropriate case, we should co nsider revisiting (or at least limiting) that specific holding from Free the Nipple. Allowing any deprivation of any constitutional right to serve as per se irreparable harm is a far-too-powerful tool in most cases.