In the wake of the shooting incident in Las Vegas last October that resulted in more than 50 people dead and hundreds injured when they were fired upon by a man who shot from his high-rise hotel room down into a crowd attending a country music concert, attention quickly turned to a little known gun accessory known as a ‘bump stock.’ These devices, when added on to any kind of semi-automatic rifle, ranging from so-called “assault weapons” such as the AR-15 to a standard hunting rifle, could effectively turn a semi-automatic weapon into something closely resembling a fully automatic weapon, which have been either completely banned or highly regulated since as long ago as the 1930s. This device came into focus largely due to the fact that it was discovered after the shooting that many of the weapons that the Las Vegas shooter had in his hotel room were equipped with such devices, although it’s unclear if any of those weapons had actually been used in the incident. Despite the fact that fully automatic weapons are either banned outright or effectively impossible for Americans to obtain due to the in-depth and expensive process that someone who wants to purchase such a weapon, the Bureau of Alcohol, Tobacco, and Firearms had ruled several years eariy that it lacked the authority to ban the devices since they did not fall within the statutory definition of an ‘automatic weapon’ and the law did not grant the Executive Branch sufficient discretion to ban the device because of the way it could potentially be used.

In part due to the shock of the size of the massacre in Las Vegas, momentum began to build in its wake for Federal Government action to ban bump stocks. Even among strong proponents of gun rights (see here, here, and here, for example) argued that there was no defensible reason for such devices to be legal, something I argued myself just a few days after the Las Vegas shooting. Many Republicans on Capitol Hill agreed, and at least publicly stated that they would be willing to move forward on Congressional action to ban the device. Additionally, polling showed that the American public as a whole was very supportive of the idea of banning these add-ons as well as other gun control measures.  It was a small step, of course, and somewhat unconnected to the gun control issues typically raised by mass shooting incidents such as the recent school shooting in Florida or the many others that have occurred over the year that didn’t involve the use of bump stocks. In any case, at the time at least, it seemed as though this would be one small issue on which everyone could agree. As it turned out, that initial optimism was misplaced. With the House and Senate both focused at the time on the Republican tax plan, the bump stock issue quickly faded from away and momentum on any kind of legislation on the issue slowed to a crawl on Capitol Hill. In the end, no action was taken on the issue and nobody seemed to notice.

Now, with the gun control debate back on the front pages thanks to the school shooting debate, Republicans are once again finding themselves largely overmatched in the public arena for the moment, the Trump Administration has decided to act on the bump stock issue:

WASHINGTON — President Trump — under pressure from angry, grieving students from a Florida high school where a gunman killed 17 people last week — ordered the Justice Department on Tuesday to issue regulations banning so-called bump stocks, which convert semiautomatic guns into automatic weapons like those used last year in the massacre of concertgoers in Las Vegas.

A day earlier, Mr. Trump signaled that he was open to supporting legislation that would modestly improve the national gun background check system, and on Tuesday night, he posted on Twitter that Democrats and Republicans “must now focus on strengthening Background Checks!”

But Mr. Trump’s first embrace as president of any gun control measures was dismissed by gun control supporters as minor. The National Rifle Association supports the background check legislation and also backs bump stock regulation, although not an outright ban.

Speaking at the White House days after a shooting at Marjory Stoneman Douglas High School, Mr. Trump said that he had directed Attorney General Jeff Sessions to develop the regulations.

“We cannot merely take actions that make us feel like we are making a difference,” Mr. Trump said at a ceremony as he conferred the medal of valor on public safety officials. “We must actually make a difference.”

(…)

The president’s bump stock announcement surprised the Bureau of Alcohol, Tobacco, Firearms and Explosives, which did not appear to have been informed of the pending remarks from Mr. Trump. The Justice Department announced a review of the devices in early December. Led by the A.T.F., the review sought to determine whether the bureau — which is responsible for policing firearms — was able to regulate the devices without action from Congress.

Under the Obama administration, the bureau had determined it could not regulate them. Given that prior position, A.T.F. officials had indicated privately in the months after the Las Vegas massacre that any ban of bump stocks would require new legislation.

Bump stocks were not used on the rifle in the shooting last week in Florida, the authorities said.

Mr. Trump’s announcement on Tuesday appeared to short-circuit the agency’s review. The A.T.F. had not yet determined whether it had the authority to ban the devices when Mr. Trump directed Mr. Sessions to draft a regulation doing so.

In a statement, an A.T.F. official said she was “not authorized to comment on pending legislation, legislative proposals or the possibility of executive action.” A Justice Department spokesman said that the department “understands this is a priority for the president.”

While this is a notable change for a Republican President, it may not be sufficient to make any progress even on this one small issue. For example, Robert Verbruggen, a conservative who supports the idea of banning bump stocks, argues, this is an issue that seems to require that Congress act rather than the Executive Branch:

I’ve said before that we should treat bump stocks the same way we treat fully automatic machine guns, given that they achieve nearly the same rate of fire and exploit a loophole in the law. I’ve also said, though — and would like to reiterate — that Congress, not the executive branch, must do this:

Federal law defines “machinegun” as a “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.” Bump stocks do not allow the weapon to fire multiple times for each function of the trigger; they just help the user pull the trigger incredibly rapidly.

The Obama administration didn’t approve the sale of bump stocks because it loved the idea; it approved the sale of bump stocks because the law on the books didn’t give it any other option. Even after the Las Vegas shooting, per the New York Times, Justice Department officials were saying — both in private and in public — that it wasn’t possible to regulate bump stocks through the executive branch, and that Congress would have to get involved.

The Volokh Conspiracy’s Jonathan Adler adds his insight on whether a regulatory ban on bump stocks can work:

The potential problem for any effort to ban bump stocks through unilateral executive action is existing federal law. 26 USC §5845(b) defines “machinegun” as follows:

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. The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun, and any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person.

At first it may seem that bump stocks can be covered because the definition expresslys include parts that can be used to turn a semi-automatic weapon into a fully automatic one — but not so fast. The problem is that the language of the statute also specifies that what makes a weapon a machine gun is the ability to fire more than one shot automatically “by a single function of the trigger.” This describes how fully automatic weapons work, but it does not describe how bump stocks operate.

While bump stocks facilitate rapid firing, they do so by rapidly and repeatedly engaging the trigger, not by enabling true automatic fire, a point Robert VerBruggen makes at NRO. In other words, a bump stock is not something that enables true automatic fire as defined by the statute. It is for this reason that bump stocks of the sort used by the Las Vegas shooter were not regulated as machineguns by the Obama Administration, which considered the question in 2013.

The Justice Department could try and argue that the relevant statutory text should be read functionally, rather than literally. That is, the government could say that this language should be understood to cover anything that simulates the rapid fire of an automatic weapon, even if it does so by the repeated function of the trigger. Further, the Department could argue that the intent of a bump stock is to “convert” a semi-automatic weapon into a fiarearm with automatic functionality, even if it does not actually “convert” a semi-automatic into one that can “shoot, automatically more than one shot . . . by a single function of the trigger.” Finally, the Department could claim that while the trigger is repeatedly engaged with a bump stock, the shooter only acts to engage the trigger once. These arguments are clever, but perhaps too clever, as they take liberties with the relevant statutory text.

I am not sufficiently knowledgeable about the intricacies of Federal law on the issue of automatic weapons and what the BATF and other Executive Branch agencies have the authority to do when it comes to issuing appropriate regulations to enforce the laws enforce the laws on the issue that Congress has passed, or whether those agencies have sufficient discretion to interpret the law as it stands to give itself the authority to ban bump stocks. That being said, the argument that Verbruggen made back in October that only Congress has the authority to act here is rather persuasive, and the fact that the Justice Department and the BATF have been researching the issue since October would seem to indicate that there is no easy answer to the question. As Verbruggen concedes in his October column, it’s possible that the BATF could decide to broadly interpret the relevant laws on automatic weapons and the authority granted to them by Congress to include the authority to ban these devices. Given the fact that Courts tend to defer to agencies such as the BATF in their interpretation of the laws that they are charged with enforcing, it’s even possible that the such a decision would withstand a court challenge. On paper, though, it seems clear that this is an area where Congress is the one that ought to be acting. Instead, it appears that Congress is once again will to cede ground to the Executive Branch rather than take a stand on a seemingly easy issue.

Update: This post was updated to include the analysis from Professor Adler, which was posted at the time this post was being written.