The Rule of Lenity and Ghost Guns: A New Digital Frontier
The Bureau of Alcohol, Tobacco, Firearms, and Explosives has faced legal challenges against its regulation regarding “ghost guns,” or unserialized firearms kits, in recent years. These challenges have all been grounded on one of the oldest principles present in the Anglo-American legal tradition, known as the “Rule of Lenity." In English common law, dating back to the 18th century, the Rule of Lenity states that if a criminal statute is enigmatic and can be interpreted in multiple ways (with two main perspectives), then the court is required to adopt the viewpoint that is favorable towards the defendant. The reason this principle was born was out of recognizable historical necessity to prevent judicial and executive tyranny. In the early Republic of America, Chief Justice John Marshall affirmed the necessity of the principle in United States v. Wiltberger (1820), in which he stated that the “power of punishment is vested in the legislative, not in the judicial department.” In essence, the rationale behind this is twofold, communicating that: in order to know something is unlawful or unconstitutional, a citizen must be able to read the law and know exactly what is illegal. If an agency like ATF were to amend or re-interpret a 1934 definition of what a firearm actually is, in order to have it entail a block of plastic/kit of parts, the average citizen would lack “fair notice.” The other main rationale is the Separation of Powers, meaning that only the person’s elected representatives (Congress) maintain the authority to define what constitutes a crime.
In line with the historical context of the National Firearms Act of 1934 and the Gun Control Act of 1968, Congress utilized specific language in its definition of “firearms” and "receivers." For decades, the understanding has been that the receiver is the part of the gun that was finished and functional. The new, 2026 legal battle attempts to protect the enduring rule that if the law doesn’t foster an explicit ban on “kits,” the government cannot interpret something as a new criminal category without Congress’s say on it. However, beyond historical contexts, the modern-day application of the Rule of Lenity has been escalating in recent years. In 2024, a Court decision by the name of Garland v. Cargill struck down, in a 6-3 ruling, the ATF’s ban on bump stocks (firearm accessories that replace a rifle’s standard stock, allowing smaller guns to operate in a way that mimics fully operational machine guns). This ban was not only on the grounds of the Second Amendment, but also via a strict statutory perspective. Notably, Justice Thomas’s majority opinion highlighted that a semi-automatic rifle equipped with a bump stock does not fit the very specific technical definition of a “machine gun” based on the National Firearms Act of 1934. The court demonstrated that the Rule of Lenity barred any agency attempts to stretch a criminal statute that had been long established to accommodate new technology.
Despite the definitive nature of the principle, as demonstrated via the Supreme Court for a long period of time, it faced a challenge in enforcement in March of 2025, with a case called Bondi v. VanDerStok, in which the Supreme Court upheld the ATF’s 2022 rule, which required serial numbers on “buy-built-shoot” kits. In this, Justice Gorsuch (who wrote for the majority) made a distinction between Vanderstock and Cargill by arguing that an almost complete firearm kit is “readily convertible” into a truly functional weapon and could therefore be made to fit into the statutory definition of a firearm. As of January 2026, a fragmented legal landscape has been fostered as a result of the aforementioned conflicts, especially as a novel wave of litigation has come to challenge whether this authority extends to digital files and 3D-printer software. The Rule of Lenity, however, suggests that if the statute doesn’t mention “software” or “code,” then the possession of either thing cannot be criminalized as a real firearm could be.
The Major Questions Doctrine and the fair notice requirements of the Due Process Clause have become the integral parts of the 2026 legal debate, as proponents of the ATF’s bolstered rules argue that the “Ghost Gun” crisis has become a matter of public safety, and there’s urgency to it. In January of 2026, states such as California and New York are pushing out mandates for “Blocking technology” for 3D printers. These states argue that the Gun Control Act intended to make sure all firearms are traceable, and if technology permits somebody to bypass a “kit” and print a frame from scratch, the agency must be provided the ability to interpret the law to make sure the “source” of the weapon is covered.
Opponents to this argue that the petitioners are suggesting “regulation by fiat.” This means if a citizen downloads a CAD file in 2026, they aren’t provided fair notice from the 1968 Gun Control Act that they owned a “firearm” to begin with. Under the Rule of Lenity, any form of ambiguity regarding whether software qualifies as a "receiver" must be taken into account in favor of the individual. Therefore, to allow an agency to bridge this gap without a new act of Congress is in violation of the separation of powers. As famously stated by Justice Scalia, "we have never thought that the interpretation of those charged with prosecuting criminal statutes is entitled to deference."
The legal chaos that has been so prominent in January 2026 effectively exhibits that the 1934 and 1968 firearm acts are no longer sufficient to govern in an era of rapidly expanding digital manufacturing. However, the Rule of Lenity remains a barrier for expansion into this digital realm, and thus, the most constitutionally sound resolution isn’t for the Courts to amend the law via creative interpretation, but rather for them to pass a more contemporary, separate act that's pertinent to digital firearms.
Bibliography
Madonna, Anthony. “National Firearms Act of 1934.” The Congress Project, 28 June 2016, www.thecongressproject.com/national-firearms-act-of-1934. Accessed January 21st, 2026.
ATF. “Gun Control Act | Bureau of Alcohol, Tobacco, Firearms and Explosives.” Atf.gov, 14 Mar. 2025, www.atf.gov/rules-and-regulations Accessed January 22nd, 2026
“Text - H.R.17735 - 90th Congress (1967-1968): Gun Control Act of 1968.” Congress.gov, 2024, www.congress.gov/bill/90th-congress/house-bill/17735/text. Accessed January 22nd, 2026
“Bondi v. Vanderstok, 604 U.S. ___ (2025).” Justia Law, 2025, supreme.justia.com/cases/federal/us/604/23-852/. Accessed January 27th, 2026
Johnson, Joel. “An Off-Ramp for the Court’s next Big Gun Case.” SCOTUSblog, 18 Dec. 2025, www.scotusblog.com/2025/12/an-off-ramp-for-the-courts-next-big-gun-case/. January 30th, 2026
“A Second Amendment Preview of the Supreme Court’s Long Conference | Duke Center for Firearms Law.” Duke Center for Firearms Law, 2025, firearmslaw.duke.edu Accessed January 31st, 2026