The fate of a ban on bump stocks is now in the hands of Congress after the Supreme Court ruled Friday that current law doesn’t allow the government to outlaw them as equivalent to machine guns.

The justices said in a 6-3 ruling that the Trump administration’s attempt to reinterpret definitions to try to shoehorn bump stocks into the current ban on machine guns won’t fly. But the justices said nothing is stopping Capitol Hill from changing to law to explicitly cover bump stocks.

Democrats were quick to take up the invitation.

“It is really critical that we continue to make sure we can keep guns out of the hands of people who shouldn’t have them,” said Rep. Debbie Wasserman Schultz, Florida Democrat.

“Send me a bill and I will sign it immediately,” President Biden said.

But conservative Republicans signaled the idea will be met with resistance.

“It was a foolish mistake under both administrations — I think this was a Trump era rule,” said Rep. Chip Roy, Texas Republican. “The court striking it down is a win for people’s Second Amendment rights.”

A bump stock is a device that attaches to the rear of a rifle, helping it quickly slide back and forth. The resulting motion helps repeatedly engage the trigger fast enough that it can simulate automatic fire.

But Justice Clarence Thomas, writing the key opinion for the court, said that doesn’t match the law’s definition of an automatic weapon, which specifies “a single function of the trigger.”

He said even with a bump stock, a rifle still requires the right amount of pressure from the hand on the barrel to operate.

“Without this ongoing manual input, a semiautomatic rifle with a bump stock will not fire multiple shots. Thus, firing multiple shots requires engaging the trigger one time — and then some,” Justice Thomas wrote.

Justice Sonia Sotomayor, writing the dissent for the three Democratic appointees, said Justice Thomas was dissecting definitions too finely. She said bump stocks seem like machine guns to her.

“When I see a bird that walks like a duck, swims like a duck, and quacks like a duck, I call that bird a duck,” she wrote.

For years, the Bureau of Alcohol, Tobacco, Firearms and Explosives had seen things the same as Justice Thomas. That changed in 2018, a year after a gunman armed with rifles outfitted with bump stocks perpetrated the worst mass shooting in modern U.S. history.

From a perch in one of the city’s hotels, he fired down at concertgoers, killing 58 people and wounding more than 500 others.

That incident prompted the Trump administration to do its rewrite.

Las Vegas also loomed large for the justices.

“All the shooter had to do was pull the trigger and press the gun forward. The bump stock did the rest,” said Justice Sotomayor.

But Justice Samuel A. Alito Jr., who joined the majority, said tragedies can’t trump the law.

“The horrible shooting spree in Las Vegas in 2017 did not change the statutory text or its meaning,” he wrote. “There is a simple remedy for the disparate treatment of bump stocks and machineguns. Congress can amend the law — and perhaps would have done so already if ATF had stuck with its earlier interpretation. Now that the situation is clear, Congress can act.”

The case was brought by Michael Cargill, owner of Central Texas Gun Works, who challenged ATF’s 2018 rule reversal. He argued the ATF violated procedural law with its attempt to change the policy on its own without going to Congress.

The 5th U.S. Circuit Court of Appeals ruled in his favor, reasoning that the government’s use of a decades-old ban on machine guns and applying that to bump stocks was ambiguous.

The Supreme Court’s decision Friday affirmed that ruling.

“This is huge for the Second Amendment community. This is huge for everyone in America. If you’re pro-gun, or anti-gun, it doesn’t matter. This is about the administrative agency,” Mr. Cargill told the Washington Times, adding an agency can’t write laws.

“It has to go back to Congress. Congress has to write the law,” he said.

That’s easier said than done, however.

Gun legislation is notoriously difficult to get through Congress, and chances are even tougher now after the experience of the last bill, in 2022.

That was the Bipartisan Safer Communities Act, passed in the wake of mass shootings in Buffalo, New York, and Uvalde, Texas, which sought to tighten rules on who could purchase and sell firearms.

Mr. Biden earlier this year released a new policy — he said to carry out the law — that makes far more firearms sales have to go through a background check.

Republicans who worked on the 2022 bill said Mr. Biden betrayed them by stretching the law beyond what they’d intended. Sen. John Cornyn, a Texas Republican who was instrumental in the negotiations, said Mr. Biden had become “a dishonest broker.”

The relatively few days Congress is in session between now and the election also means the gun issue is likely to matter less in the legislative world and more in campaign trail politics.

• Kerry Picket and Lizzie Donker contributed to this article.

• Stephen Dinan can be reached at sdinan@washingtontimes.com.

• Alex Swoyer can be reached at aswoyer@washingtontimes.com.