After Chevron fell, ATF rules lost the deference they quietly relied on

Imagine a bureaucrat tells you the plastic brace on your pistol is perfectly legal. You buy it, in reliance on the letter. A few years later the same office decides the brace turns your pistol into a short-barreled rifle, a federal felony item unless registered. Nothing in the statute changed. Congress did not vote. The agency simply reread the words and arrived at a new answer.

Now imagine a judge who says: the agency's new reading is reasonable, I will go along. That, for decades, was how federal courts treated disputes of this kind. A single phrase, "Chevron deference," explained the judge's deference. In June 2024, the Supreme Court retired it. This post explains why that is good news for anyone who owns a gun, and why the reason is not really about guns at all.

Terms first

Statute. A law passed by Congress and signed by the President. Agency rule. A regulation written by an executive agency such as the Bureau of Alcohol, Tobacco, Firearms and Explosives under authority Congress has given it. Deference. A court's practice of accepting an agency's reading of a law instead of deciding for itself what the law means. Rule of lenity. The old principle that when a criminal statute is genuinely ambiguous, the court resolves the doubt in favor of the person charged.

My thesis, which I will argue in numbered steps, is that Congress, not an agency, must write gun crimes, and that the end of Chevron deference moves the law toward that rule.

What Chevron said

Chevron U.S.A. v. Natural Resources Defense Council was decided in 1984. It involved an Environmental Protection Agency regulation about air pollution, and the Court's framework had two steps. Step one: has Congress spoken directly to the precise question? If so, that is the end of it, and the agency must follow the statute. Step two: if the statute is silent or ambiguous, is the agency's interpretation a permissible one? If it is, the court defers.

The reasoning was that ambiguity in a statute is, in effect, a delegation: Congress left a gap, and the agency, with its expertise and accountability to the President, was entitled to fill it. For forty years that logic spread into thousands of cases, and a gap in a statute came to be treated in Washington the way a vacancy sign is treated by a squatter. In National Cable & Telecommunications Association v. Brand X Internet Services (2005), the Court went further and deferred to an agency's reading of an ambiguous statute even though a court of appeals had read it differently in an earlier case. A statute meant one thing in one administration and another in the next, and the courts nodded.

The overruling

On June 28, 2024, in Loper Bright Enterprises v. Raimondo, the Supreme Court overruled Chevron by a vote of six to three. Chief Justice Roberts, writing for the majority, said that the Administrative Procedure Act of 1946 requires courts to "decide all relevant questions of law" and to interpret statutes for themselves, and that the idea that ambiguity is an implicit delegation of power to an agency was a fiction. Courts may still look to an agency's views for what the Court's earlier cases, notably Skidmore v. Swift & Co. (1944), treated as persuasive guidance, according to the thoroughness and validity of the agency's reasoning. But the final word on what a statute means belongs to the judge.

The opinion also said that where Congress has expressly delegated discretion to an agency, with words such as "appropriate" or "reasonable," a court's task is to police the boundaries of that delegation and to see that the agency has reasoned carefully within them. That nuance matters, and I will come back to it.

Marbury v. Madison (1803) said it long ago: "It is emphatically the province and duty of the judicial department to say what the law is." Loper Bright put that sentence back to work.

Why it matters doubly for the ATF

Most agencies enforce civil rules. The ATF's rules carry criminal penalties. That difference changes the analysis.

Take the National Firearms Act. Section 5845(b) of Title 26 defines a machine gun as "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." Possession of an unregistered machine gun is a federal felony, punishable by up to ten years in prison. When the ATF decides that a new device fits that definition, it is not just interpreting a regulation. It is deciding who goes to prison.

And that is a problem the Constitution takes seriously. Article I, Section 1 says: "All legislative Powers herein granted shall be vested in a Congress of the United States." Criminal law is the clearest example of legislative power, since it is the power to say what conduct the government may punish. The reason, as Madison put it in Federalist 47, is that "the accumulation of all powers, legislative, executive, and judiciary, in the same hands... may justly be pronounced the very definition of tyranny." An agency that writes the rule, enforces the rule and, under Chevron, gets its reading of the rule accepted by the court has collected two of those powers, and sometimes three.

The rule of lenity is the old protection. It says a person should have fair warning of what the law forbids, and that where Congress has not spoken clearly, the person charged gets the benefit of the doubt. A court that defers to an agency's reading of a criminal statute does the opposite. It gives the government the benefit of the doubt. In 2020, Justice Gorsuch, in a statement respecting the denial of certiorari in Guedes v. ATF, flagged the tension: the ATF's bump-stock rule had been upheld below on the strength of Chevron, and he wrote that Chevron "has no role to play when liberty is at stake." That is the heart of the matter.

How reclassification worked under the old regime

Here is the pattern, and I want to describe it with care.

The ATF administers the Gun Control Act and the National Firearms Act. Gun makers, inventors and dealers write to the agency's technical branch and ask whether a product is a firearm, a machine gun, a short-barreled rifle or something else. The agency answers in classification letters. A manufacturer who gets a favorable letter builds a business on it, and consumers buy the product.

Two well-known examples:

Bump stocks. A bump stock is a stock that uses a rifle's recoil to let the shooter fire rapidly without changing the semi-automatic mechanism. Across several administrations, the ATF concluded on more than ten occasions that bump-stock-equipped rifles were not machine guns. After the October 1, 2017 mass shooting in Las Vegas, in which a gunman used rifles fitted with bump stocks, the agency reversed itself. It issued a final rule in December 2018 declaring bump stocks to be machine guns under the statutory definition, which meant anyone who kept one after the deadline was in possession of an illegal machine gun. The Supreme Court held in Garland v. Cargill (June 14, 2024) that the ATF's reading was wrong. Justice Thomas, for a six-justice majority, held that a bump-stock-equipped semi-automatic rifle fires only one shot per "single function of the trigger," so it is not a machine gun under the statute. The Court decided it by reading the statute. It is a good illustration of what a court does when it does the reading itself.

Pistol braces. A stabilizing brace is a device that straps a pistol to the forearm. For years the ATF had told manufacturers and consumers, in a series of letters, that many braces were lawful. On January 31, 2023, the agency published a rule listing factors for deciding whether a braced pistol was a short-barreled rifle, which brought owners of braced pistols within a registration requirement or a choice between disposal and a felony. The rule was challenged in several courts, and the Fifth Circuit ruled against it in 2023 on procedural grounds. Its current status is something to check in the Federal Register and the court dockets rather than take from a blog.

What is the lesson? Under the old regime, if the statute was ambiguous, the agency's latest reasonable reading controlled. A reading could change when the administration changed. The same stock or brace could be lawful on Monday and a felony on Tuesday, with no vote in between. That is not law as the founders understood it. That is permission slips.

The other side's best argument

The counterargument deserves a fair statement, and it is not frivolous.

Congress cannot anticipate every technology. The statutes the ATF administers were written in 1934 and 1968, long before polymer frames, binary triggers and 3D printers. Someone must apply the old words to new things, and an expert agency is better suited to that than a generalist judge. Without deference, the same statute may mean different things in different circuits, and manufacturers will find loopholes faster than Congress can close them. Agencies are also politically accountable, through the President, in a way that judges are not.

I take that seriously. Here is the answer, in numbered points.

1. Technical expertise is not the same as legal authority. Loper Bright does not stop an agency from developing facts about how a device works. A judge can learn, from the agency's engineers, how a trigger functions. What the judge cannot do, and should not do, is accept the agency's view of what the words of the statute mean. Facts are the agency's strength. Meaning belongs to the courts.
2. Ambiguity is not an invitation to the executive. If Congress's words do not clearly cover a new device, the answer in a criminal case is that the conduct is not clearly a crime. That is what lenity is for. A government that wants a device to be illegal can ask Congress to say so.
3. Congress knows how to write specifics. The 1934 act listed the items it covered. The 1994 ban, which I examine in What the Justice Department's own studies found about the 1994 ban, named models and features. When Congress wants a definition, it can write one, and when the technology changes, it can amend. The inconvenience of legislating is not a defect in the Constitution. It is the Constitution. As I noted in ninety years of federal gun law in the dates that changed the rules, Congress has amended gun law many times, and each amendment was voted on.
4. Accountability runs the wrong way. The argument that agencies answer to the President sounds good until you notice that it means the meaning of a criminal law can change with each election, without a vote in Congress. The accountability the Constitution wants is accountability of the lawmaker for the law.
5. Inconsistency is a feature of a system that corrects itself. If circuits disagree about a statute, the Supreme Court resolves it, as it did in Cargill. That is slower than a memo and more reliable.
6. It cuts in both directions. A future administration, one hostile to gun rights, could use the same deference to reclassify more items. Loper Bright protects owners from an agency that wants to expand a crime, whichever party holds the White House. I would make the same argument if the shoe were on the other foot, and a principle that only protects you when your side is in power is not a principle.

What the end of deference does not do

Honest analysis requires some modesty about what has changed. Loper Bright did not invalidate any particular ATF rule. It changed the question a court asks. Rules that rest on a reasonable reading of an ambiguous statute no longer win automatically; they must be the best reading in the court's own judgment. Some will survive and some will fall. Statutes that expressly delegate authority, such as a provision allowing the Attorney General to prescribe rules "necessary to carry out the provisions" of the Gun Control Act, still give the agency room, though not unlimited room. The agency may still issue interpretive guidance, which courts may find persuasive under Skidmore. And long-settled applications of statutes, by the Loper Bright opinion's own account, keep a measure of stability from precedent.

The decision also does nothing about the Second Amendment. That is a separate wall, and I have discussed what it protects in The weapons of war argument against the AR-15 fails on its own terms. Loper Bright is about who decides what a statute means, not about whether the statute is constitutional.

What the argument comes to

Put the pieces together and the argument is short.

1. Only Congress makes law, and that includes criminal law. Article I, Section 1 vests all legislative power in Congress, and the power to define crimes is its core.
2. A person must have fair notice of what is forbidden. A criminal law that changes by memo, or that depends on how a court weighs an agency's latest preference, gives no notice.
3. Lenity is the safeguard, and deference was its opposite. Deference resolved doubts for the government. Lenity resolves them for the citizen. After Loper Bright, the courts can decide which one the Constitution favors, and I think it favors the citizen.
4. Therefore Congress must write the crime. If the old definitions do not fit a new device, Congress can pass a new one, with a vote, in the open, with its name attached.

I do not say this to make life easier for anyone who wants to evade a law. I say it because a country where the law can be changed by a letter is a country where the law is not really the law. The Founders worried about this in the form of a king who could suspend statutes. We have a more modern version, with a different title and a smaller crown. It deserves the same suspicion.

There is a practical consequence for gun owners, too. If you own a product that an agency once said was lawful, you are now in a better position to ask a court whether the later rule can survive. Reading the actual statute, which anyone can do on Congress.gov, is the first step. I have laid out the facts on one of the legal frictions at the other end of the process, the buyer's form, in Lying on Form 4473 is a felony, so why is it so rarely charged. A federal agency's power to write criminal definitions and a federal prosecutor's discretion to ignore them are two sides of the same unstable arrangement.

The case in brief

1. Chevron (1984) told courts to defer to reasonable agency readings of ambiguous statutes; Loper Bright (June 28, 2024) overruled it and returned the question of statutory meaning to judges.
2. The ATF's rules carry criminal penalties, so deference there meant the executive both defined and enforced the crime, which is exactly what the rule of lenity exists to prevent.
3. Under the old regime, items such as bump stocks and pistol braces went from lawful to felonious by agency letter and rule, without a vote in Congress.
4. Technical expertise is a good reason for courts to hear the agency's facts, but not for them to accept its view of what a law means.
5. Congress, not an agency, must write gun crimes, and the end of deference pushes the system in that direction.

What you can do: read 26 U.S.C. 5845 on Congress.gov, then write your representative and ask them to pass clear definitions of any firearm term they think needs updating, rather than leaving it to a rule.