The debate over these gun accessories first flared up after the shooter in Las Vegas, who fired into a crowd of concertgoers and killed 58, modified a semiautomatic rifle with a bump stock.

While Nikolas Cruz — who shot and killed 17 students and faculty at Marjory Stoneman Douglas High School in Parkland, Fla. on Feb. 14 — did not use a bump stock, calls to ban or regulate the attachments have resurfaced in the wake of the school shooting.

The issue does seem to be one facet of the gun control debate where conservatives and liberals may be able to agree. Everyone from Diane Feinstein to the National Rifle Association has said bump stocks should be regulated.

What is a bump stock?

A bump stock, also called a bump-fire stock, is an attachment that makes a semi-automatic weapon — like an AR-15 rifle — shoot nearly as fast as fully-automatic machine guns. This accessory replaces the standard stock on a rifle with a piece of plastic or metal molded to the lower end of the gun. This harnesses the gun’s natural recoil, allowing it to slide back and forth freely and rapidly and re-cock after each round fired.

There are other devices that allow guns to simulate automatic firing on a semi-automatic weapon, but bump stocks are the most well known of the legal options.

“The classification of these devices depends on whether they mechanically alter the function of the firearm to fire fully automatic,” Jill Snyder, a special agent in charge at the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), said at a news conference in Las Vegas following the shooting there in October. “Bump-fire stocks, while simulating automatic fire, do not actually alter the firearm to fire automatically, making them legal under current federal law.”

Still, this is more of a technicality than a significant difference in the amount of damage possible with a bump stock. A fully automatic weapon shoots about 14 rounds per second. Using a bump stock with a semi automatic AR-15 gave the Las Vegas shooter the ability to fire about 9 shots per second, according to analysis of footage by the New York Times.

Who sells bump stocks?

Slide Fire is the primary manufacturer of bump stocks.

The Texas-based company stopped producing the accessory in October 2017 after it was found that the Las Vegas shooter used a bump stock.

“We have temporarily suspended accepting new orders while we work to replenish inventory,” Slide Fire said on its website at the time.

Several other companies pulled bump stocks from their offerings following the tragedy in Las Vegas.

Cabela’s, a hunting and fishing retailer that was acquired by Bass Pro Shops in October 2017, announced that it would no longer sell the attachments. Walmart also removed bump stocks from its online store. Bass Pro noted that the company has never sold the gun accessories.

Slide Fire resumed selling bump stocks in November. Following the news that Trump called for a ban on them, gun enthusiasts rushed to put in orders and Slide Fire’s site crashed due to the high traffic.

Did Trump ban bump stocks?

On Tuesday, President Trump ordered the Justice Department to issue regulations that would ban bump stocks, after pressure to do more to curtail access to deadly weapons following the Florida shooting.

This is the first time the president has weighed in on the issue, but the Justice Department announced they would look into bump stocks as part of a review process on the legal definition of machine guns following the Las Vegas shooting. That review is ongoing in the ATF.

Trump also tweeted Tuesday about strengthening background checks, indicating that he may support modest gun control measures.

Whether we are Republican or Democrat, we must now focus on strengthening Background Checks!

— Donald J. Trump (@realDonaldTrump) February 21, 2018

Press Secretary Sarah Sanders said the White House has not “closed the door on any front” when asked about a broader ban on assault weapons on Feb. 20. The president’s recent comments on the possibility of new gun control reforms must be measured against his pledges to gun advocates in the past.

“To the NRA, I can proudly say I will never, ever let you down.” Trump said at the group’s annual convention in April 2017. The group enthusiastically endorsed Mr. Trump and spent $30 million on his campaign.

Have there been other proposed bans on bump stocks?

The term often comes up in Congressional statements and proposed legislation following mass shootings, whether or not bump stocks were used.

Even the NRA supported measures to regulate bump stock sales following the Las Vegas shooting.

The price of bump stocks rises each time a ban is proposed, with sales often doubling or tripling as support for regulation grows.

Sen. Dianne Feinstein (D-Calif.) introduced legislation to ban the import, sale, manufacturing, transfer, and possession of bump stocks and other similar gun accessories.

“The only reason to modify a gun is to kill as many people as possible in as short a time as possible,” Feinstein said.

Republican lawmakers seem to be on board this time around, with House Speaker Paul Ryan (R-Wis.) saying “ obviously we need to look at how we can tighten up the compliance” with existing laws that ban fully automatic weapons.