On Friday, the Supreme Court refused to block the Trump administration’s ban on bump stocks, which allow semi-automatic weapons to fire in rapid succession like a machine gun. Only Justices Clarence Thomas and Neil Gorsuch publicly dissented from the court’s decision, which means that bump stocks are now officially illegal in the entire United States.

The perpetrator of the 2017 Las Vegas shooting—the worst in American history, in which 58 people were killed and 400 injured by gunfire—employed a bump stock. He used 13 rifles outfitted with bump stocks to fire 1,049 rounds in just 10 minutes. In November 2018, the Trump administration announced that it would issue a new regulation interpreting a federal machine gun ban to encompass bump stocks. The rule required owners of these devices to surrender or destroy them. No bump stocks would be grandfathered in, and anyone who continued to own the device after March 26, 2019, would be committing a federal felony.

Gun rights groups quickly filed suit, alleging, among other things, that the federal statute prohibiting machine guns could not be plausibly read to cover bump stocks, as well. A federal district court ruled against the plaintiffs in February, and on Monday, the U.S. Court of Appeals for the District of Columbia Circuit affirmed that decision by a 2–1 vote. The majority held that the federal “machine gun” ban is genuinely ambiguous, requiring courts to defer to executive branch’s interpretation of the law. (This principle is known as Chevron deference.)

The dispute revolves around a provision of the statute that mandates a weapon cannot fire more than one shot “by a single function of the trigger.” A bump stock harnesses a rifle’s recoil energy to make the trigger reengage repeatedly once the shooter has pulled the trigger once. If the plaintiffs are correct, then bump stocks do not fall under the federal statute, because the trigger itself reengages with each shot. If the government is correct, bump stocks can be banned, because the shooter need only pull the trigger once to fire multiple rounds. Applying Chevron deference, the D.C. Circuit found that the government’s interpretation is perfectly reasonable and thus upheld the new rule.

The plaintiffs plan to appeal that decision, but with Friday’s ruling, the Supreme Court declined to keep the ban on hold as they do so—a likely indication that a majority of the court does not believe the rule is unlawful. There are two possible reasons why Thomas and Gorsuch may have dissented. First, there is a chance the two justices believe the rule violates the Second Amendment; both are gun rights extremists, and Thomas has written that any “types of firearms commonly used for a lawful purpose” may not be constitutionally outlawed.

Before the new rule, Americans owned about 520,000 bump stocks, which were legal in most of the country. Perhaps these justices believe that bump stocks are “commonly used for lawful purposes” and therefore protected by the Second Amendment.

Second, Thomas and Gorsuch may be irritated that the D.C. Circuit upheld the rule by applying Chevron deference. Both justices publicly oppose this doctrine, which they recently decried as “letting an interested party [an executive branch agency] … dictate an inferior interpretation of the law that may be more the product of politics than a scrupulous reading of the statute.” Thomas and Gorsuch would prefer that a court “buckles down to its job of saying what the law is” without deferring to the government’s reading of an ambiguous measure. By deferring to the Trump administration’s view of the federal machine gun ban, the D.C. Circuit surely rankled both justices.

Regardless of the dissenters’ views, it’s apparent that there is little appetite by a majority of the court to protect a device that aided a recent, horrific, and notorious massacre. Chief Justice John Roberts, Justice Samuel Alito, and Justice Brett Kavanaugh do not seem eager to use this case to bolster the Second Amendment or curtail Chevron deference. And so hundreds of thousands of gun owners will now need to dispose of their bump stocks—or become federal criminals.