The Trump Administration is setting the stage for a furious legal battle over bump stocks by proposing a rule to effectively ban the devices, which allow semi-automatic weapons to fire more rapidly.

Bump stocks were catapulted to the forefront of the debate over gun control after a man in Las Vegas killed 58 people and wounded more than 500 others by opening fire with semi-automatic weapons that used the devices.

The Las Vegas killings represent the worst mass-shooting incident in modern U.S. history, and led to immediate calls for the banning of bump stocks.

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But gun rights groups and other advocates say it’s outside the administration’s regulatory authority to ban bump stocks — and that doing so will provoke lawsuits.

The reason is complicated and has to do with how the law defines how a machine gun operates.

Machine guns are all but completely banned under a 1986 law passed by Congress that banned the possession or transfer of automatic weapons manufactured after that year.

A previous law from 1934 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 pull of the trigger. It includes any combination of parts designed and intended to convert a weapon into a machine gun.

Those arguing the administration does not have the power to ban bump stocks say the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is effectively adding to and changing the definition of a machine gun.

They say the ATF does not have that power, and that only Congress can change how a machine gun is defined.

“What Congress has banned is machine guns and that’s defined as a device that fires more than one round with the single function of a trigger,” said Adam Winkler, a professor at the University of California, Los Angeles School of Law. “The bureau can only interpret that language, they can’t add to it.”

Even within the ATF, there have been doubts that it can promulgate a rule to ban bump stocks, which attach to the stock of a semi-automatic firearm and enhance the rate at which a shooter can pull the trigger on the firearm.

While the part increases the rate of fire in a way that is close to mimicking a machine gun, groups say that does not make it a machine gun and that it was specifically created by manufacturers as a way to work around the law.

Michael Bouchard, president of the ATF Association ­— a group of former and current ATF employees — argues the best and quickest way to ban bump stocks is through legislation.

"The regulatory method takes months and is subject to legal challenges for every device made," said Bouchard, who worked at the ATF for 20 years, the last three as ATF’s assistant director.

That argument isn’t stopping the Trump administration.

Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE announced Friday the Department of Justice will soon start accepting public comments on a proposed rule to define machine gun to include bump stock devices — effectively banning them.

“After the senseless attack in Las Vegas, this proposed rule is a critical step in our effort to reduce the threat of gun violence that is in keeping with the Constitution and the laws passed by Congress,” Sessions said.

The ATF’s rule would clarify that " 'bump fire' stocks, slide-fire devices and devices with certain similar characteristics are 'machine guns' " under the federal law “because such devices allow a shooter of a semiautomatic firearm to initiate a continuous firing cycle with a single pull of the trigger.”

While the National Rifle Association has backed further regulations of bump stock, other groups are already mulling their options.

“We may very well do it,” Dudley Brown, president of the National Association for Gun Rights, said of a possible lawsuit.

“Even the ATF knows that it’s not really within their bounds to ban bump stocks,” he said.

Some gun control advocates, on the other hand, argue it is within the government’s right to regulate an end to bump stocks.

In comments to the agency in January, Everytown for Gun Safety said the 1934 law was written to be a broad regulation covering automatic firearms and the ATF has the authority to clarify which bump stocks and other conversion devices qualify as “machine guns.”

“The authority has existed to regulate these devices and in fact ATF’s job is to say which devices count as machine guns and make it clear they are not legal,” said Jonas Oransky, Everytown’s deputy legal director. “They have not previously done that in a comprehensive way.”

But David Chipman, a retired ATF agent who now serves as a senior policy adviser at the Giffords Law Center to Prevent Gun Violence, said the public is entirely missing the mark in the bump stocks debate.

He said the question is not whether the ATF has the legal authority to ban bump stocks, but why Congress has failed to act.