On Tuesday afternoon, President Donald Trump signed a memo directing Attorney General Jeff Sessions to propose a regulation making bump stocks for guns illegal. Bump stocks are used to make semiautomatic weapons fire bullets at such a rapid rate they essentially become machine guns; Las Vegas shooter Stephen Paddock used them to shoot 422 people last October.

In some small sense, it’s a victory for the gun-control movement that Trump felt sufficiently pressured in the wake of the Parkland school shooting to make at least a motion towards tightening gun laws. But that’s what this is—an empty gesture that in all likelihood will not stop bump stocks from being sold.

Federal agencies have for several years now tried to ban bump stocks, dating back to the Obama administration. (Trump, unable to pass up a dig at his predecessor, actually noted in his memo that “Although the Obama Administration repeatedly concluded that particular bump stock type devices were lawful to purchase and possess, I sought further clarification of the law restricting fully automatic machine guns.”) Last December, following the Las Vegas shooting, the Department of Justice and the Bureau of Alcohol, Tobacco and Firearms announced that it would yet again review the law and investigate whether bump stocks might be banned. It asked for public comment on a potential rule, and that comment period closed on January 18.

That’s the first thing to understand about Trump’s announcement Tuesday: he just re-announced an existing review process. The memo instructs Sessions to “dedicate all available resources to complete the review of the comments received, and, as expeditiously as possible, to propose for notice and comment a rule banning all devices that turn legal weapons into machineguns.” That was already going to happen; the most Trump did was nudge Sessions along.

But there’s a reason the Bureau of Alcohol, Tobacco, and Firearms concluded it couldn’t ban bump stocks under Obama, who was no friend of the gun lobby: bump stocks don’t appear to violate federal law. Banned machine guns are defined in the National Firearms Act 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 function of the trigger.” Bump stocks do not modify a weapon’s trigger nor make it fire automatically with a “single function.” Rather, they use the natural recoil of a gun to bounce the weapon off the shooter’s shoulder and back onto his or her trigger finger.

This may seem like a meaningless distinction, but the law is the law, and it does not appear to prohibit this type of modification. The executive branch can’t simply declare something illegal without statutory authority. Congress will ultimately need to change the law to specifically ban bump stocks.

Justice Department officials have been saying exactly that “publicly and privately” for months, according to a New York Times report late last year. According to the Times, top DOJ officials told Senate Judiciary Committee staffers outright in a closed-door meeting that the bump-stock regulation would go nowhere because ultimately an act of Congress is needed. The acting director of the ATF told a law-enforcement conference the same thing in October.

Trump notably did not call on Congress to act on bump stocks in his public announcement of the memo. He probably wants to avoid a congressional fight with the NRA, which opposes any bump stock bills in Congress. A more cynical interpretation might be that Trump and the NRA are electing to pursue a process they both know can’t go anywhere. Either way, Trump’s memo isn’t going to change anything.