For years, the conservative defense against gun control came down to a single sentence: The only way to stop a bad guy with a gun is with a good guy with a gun.

That was the formulation crafted by Wayne LaPierre, the executive vice president of the National Rifle Association, which he often cited after any mass killing that provoked new calls for tighter regulation of gun sales.

It held up after 26 children and teachers were killed in Connecticut in December 2012, with efforts to impose stricter background checks floundering in the Senate a few months later. It held up in summer 2016, after the mass murder of 49 people in an Orlando nightclub, when no debate was held on gun laws.

And again this past summer, when a gunman tried to kill dozens of Republicans practicing for the annual Congressional Baseball Game.

But this week's mass murder of 58 concertgoers in Las Vegas has shifted the tone among GOP lawmakers unlike any other mass shooting of the past decade. From House Speaker Paul D. Ryan (R-Wis.) to rank-and-file lawmakers from rural districts, there is a new openness to discussing limits on the type of accessories that can turn a gun into an automatic weapon.

The question is whether these Republicans are just positioning themselves for political cover or whether they are seeking a legitimate outcome. One thing that conservatives did was to profess their ignorance about "bump stocks," the device Stephen Paddock used on his AR-15-type rifles to essentially automate them and unload round after round from his Mandalay Bay hotel room above the country music festival.

"I didn't even know what they were until this week, and I'm an avid sportsman," Ryan said Thursday in an interview to be aired Saturday on MSNBC's "Hugh Hewitt." He said he was "quickly coming up to speed" on the issue.

"Apparently, this allows you to take a semiautomatic, turn it into a fully automatic. So clearly that's something we need to look into," Ryan said.

"Never heard of it," Rep. Ryan Costello (R-Pa.) told reporters Thursday, suggesting that he was open to something that would outlaw the devices.

One bill, offered by Rep. Carlos Curbello, a Republican from a South Florida swing district, was a narrower version of legislation offered by Sen. Dianne Feinstein (D-Calif.) to ban many accessories for semiautomatic weapons.

But even the most organized, well-intended efforts at gun restrictions in recent years have faded away in the weeks after the nation moves on from each tragedy, losing political momentum and giving the NRA time to shore up its defenses.

Perhaps that's why two junior Republicans, Reps. Adam Kinzinger (R-Ill.) and Mike Gallagher (R-Wis.), have taken a different route and are gathering bipartisan signatures for a letter asking the Bureau of Alcohol, Tobacco, Firearms and Explosives to ban these devices through a regulatory decision.

They believe that if this goes through Congress, it will get bogged down in the details of trying to define which devices get outlawed, and the outcome will be in doubt. "Let's be honest about what would happen with the legislative solution. We're going to be naming devices and things in Congress. That's going to lead to a lot of debate," Kinzinger told reporters Thursday.

Even if successful, such a bill would probably end up watered down and leave new devices making similar changes to guns not on the list of outlawed products. Instead, the two Republicans want ATF to issue a ruling based on "the spirit of the law" that outlaws automatic weapons, believing that Congress will never get it right.

"If the ATF comes to the ruling that the spirit of the law matters, then that would be effective for future devices," Kinzinger said.

It's remarkable enough to have Republicans pushing for more regulations of any industry, when the GOP controls all the levers of Washington power.

It's also an important signal that Kinzinger and Gallagher are leading the effort. They are both loyal allies of Ryan and veterans of the wars in Iraq and Afghanistan. Kinzinger is still in the Air National Guard, and Gallagher was a Marine intelligence officer in Iraq.

The regulatory route through ATF might be the best chance to restrict bump stocks and other devices that could be used in mass killings.

Rep. Bob Goodlatte (R-Va.), chairman of the House Judiciary Committee, indicated that he wanted to review the matter legislatively. "We're going to look at the issue," he told The Washington Post's Mike DeBonis.

But the Judiciary Committee has been something resembling a legislative wasteland when it comes to bipartisan accomplishments. Goodlatte began work four years ago on a bipartisan bill to grant permanent legal status to hundreds of thousands of undocumented immigrants brought to the United States illegally when they were children.

It garnered so little support that the bill was never formally introduced.

What could be different about the Las Vegas situation? The sheer nature of the terror.

"I have a personal concern about what happened," Goodlatte said.

Because lawmakers, Republicans and Democrats alike, seemed to agree that in this instance, a good guy with a gun would not have been able to do very much.

Paddock was 32 floors above the ground, with 23 guns, a dozen of them rigged to fire like fully automatic weapons, at night. Las Vegas police down below did not know where the bullets were coming from, nor did security inside the hotel. It took an hour to take down the shooter.

It was not a fair fight, and a good guy with one gun would have been entirely outmatched.

"I'm a gun owner, multiple guns myself, but at the same time I agree that civilians shouldn't have access . . . to fully automatic weapons," Kinzinger said.

"Absolutely, we need to take action," he added.

It's still an open question whether Congress can figure out how to do that.

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