By Dianne Feinstein

Originally published in The Washington Post.

The Justice Department issued a regulation Tuesday banning bump-fire stocks, devices that can essentially transform semiautomatic weapons, such as an AR-15, into automatic rifles that fire at a rate of between 400 and 800 rounds per minute. These devices can inflict absolute carnage, as they did in October 2017, when a gunman killed 58 people at a concert in Las Vegas.

Support for banning bump stocks is widespread, and it’s encouraging to see the Trump administration take action on gun safety.

But let’s not celebrate too quickly. Presidents can rescind regulations just as easily as they create them, and in this case, the bump stock ban will likely be tied up in court for years. Only hours after the Trump administration released its final regulation, Gun Owners of America announced it would file a lawsuit.

To ensure a ban is implemented and protected from legal challenges, Congress must still pass a law banning bump stocks and other similar devices, such as trigger cranks.

The sale and manufacture of automatic weapons have been illegal since the National Firearms Act was updated in 1986. The law — even though it eased restrictions on most guns by allowing interstate sales of long guns and removing requirements to record ammunition sales — made clear that civilians should not have such weapons.

Automatic weapons produced before 1986 are highly regulated, and the Bureau of Alcohol, Tobacco, Firearms and Explosives tracks them. Despite this, the agency has consistently stated that bump stocks could not be regulated under the current law. That was because they do not fit the legal definition of an automatic weapon under the National Firearms Act.

Automatic weapons are defined by their ability to fire a continuous number of rounds by holding down the trigger. Bump stocks and other accessories have made this definition largely obsolete, creating a loophole that circumvents Congress’s intent to bar civilians from achieving automatic rates of fire. That’s because the recoil of the stock “bumps” the finger against the trigger, allowing the weapon to achieve automatic fire. Because of this technicality, bump stocks have not run afoul of the law.

ATF initially concluded that it could not ban these devices through regulation in 2008. And after the 2012 shooting at a movie theater in Aurora, Colo., ATF further explained in a 2013 letter to Congress that it could not take unilateral action because “stocks of this type are not subject to the provisions of federal firearms statutes.” In addition, internal ATF documents made public through Freedom of Information Act requests by Giffords Law Center and Democracy Forward show that the agency had reiterated its lack of authority to ban bump stocks unilaterally and that it had approved similar devices as recently as April 2017 — under the Trump administration.

In March 2018, the Justice Department did an about-face, claiming that bump stocks do, in fact, fall under the legal definition of a machine gun and therefore can be banned through regulations. The administration’s position hinges on a dubious analysis claiming that bumping the trigger is not the same as pulling it.

Reversing the agency’s statutory interpretation leaves this new regulation especially vulnerable to legal challenges, particularly given that it held the same position under the Trump administration as the Obama administration. Further, the Justice Department laid out potential legal and constitutional challenges to the regulation in a 157-page report, providing a road map for the gun lobby to challenge it.

Even ATF Director Thomas Brandon acknowledged in a Judiciary Committee hearing earlier this year that banning bump stocks through regulation would likely be challenged in court, and the best way to achieve a ban on bump stocks would be to pass a law. He said that the “optimum answer for public safety, as a career guy [for] 30 years, the law is clearly the best route.”

Both Justice Department and ATF lawyers know that legislation is the only way to ban bump stocks in a way that will not be tied up in court for years. The National Firearms Act has not changed since 1986, and it must be amended to cover bump stocks and other dangerous devices like trigger cranks.

Legislation would achieve the goals both Democrats and Republicans say they want to achieve — getting these dangerous devices off the streets. Members of Congress should not rest until our communities are safer and we no longer have to worry about a single gunman having the power to kill more people in a matter of minutes than assault weapons used to kill in an entire year.

Dianne Feinstein, a Democrat, represents California in the U.S. Senate.