Washington • In the days after a gunman shot and killed 58 people on the Las Vegas Strip, officials inside the Justice Department scrambled to address a question thrust to the center of public debate: Could anything be done to regulate the device that enabled the shooter to fire his weapons as though they were automatic?

The Bureau of Alcohol, Tobacco, Firearms and Explosives had years earlier decided it could not under existing law restrict the device, known as a bump stock. But the agency was being asked by the Trump administrationto reconsider.

"What's the earliest possible time we can get ATF's analysis?" a Justice Department official wrote to an ATF assistant director in October, four days after the shooting. "Getting a lot of pressure to get have an answer."

Weeks of debate followed and, even now, in the wake of another mass shooting at a Florida high school, bump stocks remain legal and outside of ATF's regulatory reach. Critics of the administration fear that a similar pattern might play out again: The department will never ban the devices and, even if it does, officials will face a difficult and costly court battle to make their decree stick.

Justice Department officials say that after the October shooting, they initiated a process that will probably ban bump stocks. And this week, President Donald Trump increased the pressure, commanding his attorney general to move as quickly as possible.

A spokeswoman for Attorney General Jeff Sessions said he is fulfilling the president's request.

"The Attorney General is acting expeditiously to conduct a rulemaking process that will, consistent with the law, amend the regulations to prohibit bump stock devices that turn legal weapons into machineguns," Justice Department spokeswoman Sarah Isgur Flores said in a statement.

The debate over bump stocks is, in ways, emblematic of the larger gun-control debate: pitting political will against institutional red tape, and optics against substance. Nikolas Cruz, the 19-year-old charged with killing 17 people at Marjory Stoneman Douglas High School in Parkland, Florida, did not use a bump stock. And Congress could at any moment pass legislation that would obviate the need for ATF action.

Bump stocks began receiving significant attention in October, after Stephen Paddock used the devices to rain terror on concertgoers on the Strip. The small attachments effectively turn a semiautomatic weapon into a machine gun, using a gun's recoil against a shooter's trigger finger to dramatically speed up the fire rate.

ATF has the authority to regulate machine guns or devices that create them. And the National Rifle Association, notably, does not oppose ATF's acting on bump stocks under existing law — although it has objected to new legislation aimed at the same effect.

"There's already a law, so they should regulate it under the current law," said NRA spokeswoman Jennifer Baker, adding that the proposed legislation was overly broad and might affect other devices.

In the past, ATF officials have concluded that they cannot act on bump stocks because of the way they function. That is because federal law defines a machine gun as a weapon that fires more than one shot with "a single function of the trigger." And current iterations of the bump stock, while simulating that result, technically involve multiple trigger pulls.

"In essence, the bump stock is helping pull the trigger for you," said former ATF assistant director Michael Bouchard, now president of the ATF Association.

That is not to say ATF couldn't change its mind. Just days after the Vegas shooting, the Justice Department pushed ATF officials for new analysis, according to emails obtained by the advocacy group Democracy Forward, which, on behalf of the Giffords Law Center to Prevent Gun Violence, had filed a Freedom of Information Act request and then a lawsuit for the documents.

The emails, which are heavily redacted, show that ATF produced a memo outlining its analysis on Oct. 5. A week later, the agency briefed congressional staff members. Sen. Dianne Feinstein, D-Calif., said in a statement that ATF at that point "explained why the agency concluded that it lacks the authority to ban bump-fire stocks and similar accessories," and that is why she was pushing for legislation to regulate them.

Behind the scenes, the Justice Department's Office of Legal Counsel — which reviews all orders of the attorney general and regulations requiring the attorney general's approval — was working on its own analysis, a Justice Department official said. And in December, Sessions announced that he was initiating the process to potentially change federal regulations on bump stocks and would be accepting public comments through Jan. 25.

Acting ATF Director Thomas Brandon said at a congressional hearing the next day that although he could not guarantee the agency would ultimately conclude it had the power to regulate the devices, that was on the table.

"If that wasn't a possibility at the end, we wouldn't initiate this process," he said.

Democrats, meanwhile, have renewed their calls for legislation banning bump stocks in the aftermath of the Florida shooting, and Sen. Marco Rubio, R-Fla., said at CNN's town hall on gun violence this week that he would support such a measure.

That would be more effective than regulation, Bouchard said, because it would subvert possible legal challenges and potentially offer clarity on what to do with bump stocks that already have been sold or new devices designed to get around the regulation. Manufacturers — who did not return messages seeking comment — have continued to aggressively market and sell bump stocks.

"The next step is you'll have lawsuits against the government, and we're going to be spending tax dollars to defend these decisions, when we wouldn't have to spend any money if Congress just changed the language," Bouchard said of a possible regulatory move.

Those critical of the administration say, too, that officials seem to be slow-walking the process when, on other policies, they have moved rapidly without any public input. Although the period for comments closed a month ago, the Justice Department has yet to take any action, and the next step is most likely to issue a rule that will be subject to more public comment and debate.

"How many more people are going to die in this extremely lengthy rulemaking process?" said Tyson Brody, Democracy Forward's research and investigations director, adding, "It's like a tragic deja vu."

The Washington Post's Julie Tate contributed to this report.