Today President Trump said he plans to prohibit bump stocks by executive order, notwithstanding the lack of legal authority to impose such an administrative ban. "We can do that with an executive order," Trump told Sen. John Cornyn (R-Texas). "I'm going to write the bump stock, essentially, write it out. So you won't have to worry about bump stock[s]. Shortly that will be gone." Trump's determination to ban bump stocks by administrative fiat is a blatantly political attack on the rule of law that conservatives would have immediately condemned as such if Barack Obama had attempted it.

Bump stocks are accessories that increase a rifle's rate of fire by harnessing recoil energy to help the shooter slide the weapon back and forth against his trigger finger. Previously an obscure novelty, they became notorious after they were used in the mass shooting that killed 58 people in Las Vegas last year. People who had never heard of bump stocks before, including conservatives who are otherwise leery of gun control, were suddenly clamoring for a ban. Even the National Rifle Association seemed to favor a ban, urging the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to "immediately review whether these devices comply with federal law." Talk of banning bump stocks picked up again after this month's mass shooting at a high school in Florida, although that attack did not involve bump stocks.

While bump stocks became a bête noire of the anti-gun movement only recently, they were never the sort of product that gun controllers would happily tolerate. It is therefore telling that the Obama administration, which was much less supportive of gun rights than the Trump administration, never tried to restrict bump stocks. To the contrary, the ATF during the Obama administration repeatedly affirmed their legality—in a 2010 letter to Slide Fire Solutions, which makes one version; a 2012 letter to a competing company, Bump Fire Systems; and a 2013 response to an inquiry from Rep. Ed Perlmutter (D-Colo.). As the agency explained to Perlmutter, "Bump-fire stocks (such as the Slide Fire Solutions stock) that ATF determined to be unable to convert a weapon to shoot automatically were not classified as machineguns."

Trump is unfazed by the ATF's legal logic. He wants to ban bump stocks as a symbolic gesture against mass shootings and instructed Attorney General Jeff Sessions to find a way. "We will have an announcement on that soon," Sessions said yesterday while addressing the National Association of Attorneys General. "We believe in that, and we have had to deal with previous ATF legal opinions, but our top people in the Department of Justice have believed for some time that we can through regulatory process not allow the bump stock to convert a weapon from a semiautomatic to a fully automatic."

The problem, as the ATF pointed out, is that bump stocks don't "convert a weapon from a semiautomatic to a fully automatic." If they did, the result would be a machine gun, which cannot be legally produced for civilians. But the National Firearms Act defines a "machinegun" as a weapon that fires more than once "by a single function of the trigger." A rifle equipped with a bump stock does not fit that definition, since it still fires just once per trigger pull.

Are there creative ways to overcome this difficulty? Case Western Reserve law professor Jonathan Adler suggested a few possibilities last week at The Volokh Conspiracy. "These arguments are clever, but perhaps too clever, as they take liberties with the relevant statutory text," he wrote. "If the Justice Department goes forward, and the new interpretation is challenged, these arguments might hold up in federal court, but it's a calculated risk. If the Administration truly wants to see bump stocks treated like those devices that do convert semi-automatics into machine guns, the safer and more direct route is to seek action by Congress."

The route Trump has chosen is not just indirect and uncertain; it is dishonest and unprincipled. Sessions presents himself as a law-and-order conservative, keen to enforce federal statutes and defend the Constitution, which includes respecting the separation of powers. As Rep. Thomas Massie (R-Ky.), leader of the Congressional Second Amendment Caucus, pointed out during the last debate about an adminstrative ban on bump stocks, "It is the height of legislative malpractice to ask the executive branch to legislate. We're asking the ATF and the president to do our job."

Instead of upholding the law as written by Congress, Sessions is twisting it to fit his boss's political agenda. Trump needs a concession to "common-sense gun control" that won't alienate the NRA. Sessions is determined to give him one, no matter what the law says.