The mass shooting that killed at least 59 people in Las Vegas on Sunday night is expected to rekindle the debate in Congress over federal gun control. But recent efforts in the Republican-led House have centered around loosening firearms laws, not tightening them.

Acts of mass gun violence, including last year's massacre at an Orlando nightclub and the June shooting at a congressional GOP baseball practice in Northern Virginia, have done little to change the sharp partisan divide on the issue. Most Democrats argue that the incidents heighten the need for tighter gun laws, while most Republicans say Americans should have a greater ability to protect themselves.

Last month, a House committee advanced a bill, the Sportsmen's Heritage and Recreational Enhancement Act, that would make it easier to buy firearm silencers, which are treated akin to machine guns and explosives by federal authorities. Advocates of the measure, including the National Rifle Association, have cast it as a safety enhancement.

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"The bill streamlines outmoded processes for acquiring this equipment to reduce hearing damage for sportsmen and noise at shooting ranges near residential areas," said a summary prepared by the House Natural Resources Committee, which passed the bill on a party-line vote last month. It has not yet been scheduled for a floor vote.

The legislation also includes provisions that would loosen restrictions on transporting firearms across state lines and prevent certain types of ammunition from being designated as "armor-piercing" and thus subject to tighter federal oversight.

Opponents of the measure say that the silencer provision, in particular, could make it harder to identify a shooter during an incident such as the one in Las Vegas.

"Hunters need armor-piercing bullets? They need silencers?" House Minority Leader Nancy Pelosi (D-Calif.) told reporters last month. "If you can hear, you can run to where the tragedy is emanating from."

Republicans familiar with the bill's prospects in the House said the legislation was already facing unease from moderate Republicans, and Sunday's violence only made its quick passage more unlikely.

Rep. Jeff Duncan (R-S.C.), the bill's sponsor, said in an interview Monday that the silencer provision would have had little bearing on the events in Las Vegas — pointing to media reports that the shooter may have had more than a dozen firearms, some of which may have been illegal.

"He's already breaking the law shooting an automatic weapon that wasn't registered, so what's going to stop him, had he chosen to shoot a suppressed weapon, to do that?" Duncan said. "The thing is, and the thing he probably realized is, it doesn't make any difference — it's still loud."

Bills that have been introduced this Congress propose other rollbacks to federal gun laws, including measures that would mandate that a concealed-carry permit issued in one state be honored in all other states. But those bills have not proceeded as far as the silencer legislation.

Republicans who reacted to the violence in Las Vegas early Monday did not call for any legislative response to the shooting. Law enforcement officials have not released details about the types of weapons that were used or whether they were obtained legally.

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Videos of the initial gunfire in Las Vegas appeared to indicate the use of a fully automatic, machine-gun-type weapon. Such firearms are tightly regulated by the federal Bureau of Alcohol, Tobacco, Firearms and Explosives and require a special license to own. Weapons of that type manufactured after 1986 generally cannot be privately owned.

"I mean, I heard the recording on the television: That was a fully automatic machine gun he was using, which is illegal," said Rep. Trent Franks (R-Ariz.). "And so the notion of passing another bill to make it illegal would be of little consequence."

House Majority Whip Steve Scalise (R-La.), who was gravely wounded by the gunman who attacked Republicans at the baseball practice in June, called the Las Vegas attack an "act of pure evil" and thanked those who responded and aided the victims.

"In this tragic moment, I encourage people across America to stand together in solidarity, and to support the Las Vegas community and all of those affected, especially by giving blood and encouraging others to do the same," he said. "In the face of unspeakable evil, our whole nation must respond with countless acts of kindness, warmth and generosity."

House Speaker Paul D. Ryan (R-Wis.) said that the tragedy "horrifies us all" and that the "whole country stands united in our shock, in our condolences, and in our prayers."

But Democrats quickly moved beyond well-wishes to call for legislative action, even without full details about the shooter and his motives. Pelosi, for instance, called on Ryan to impanel a bipartisan special committee to write "common sense legislation to help end this crisis."

Former congresswoman Gabrielle Giffords (D-Ariz.), who suffered serious brain damage after she was shot at a Tucson constituent event in 2011, canceled planned campaign appearances for Democratic Virginia gubernatorial candidate Ralph Northam on Monday to appear on Capitol Hill alongside her husband, retired astronaut Mark Kelly.

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Kelly, who leads the gun-control group Americans for Responsible Solutions with Giffords, called the incident "domestic terrorism" and criticized the pending Republican gun bills. He said more needs to be done to expand background checks, tighten access to the deadliest firearms and prevent domestic abusers from buying guns.

"Imagine how much worse last night's shooting could have been if the gunman had a silencer," Kelly said. "Imagine the confusion for first responders if they arrived on the scene to a bunch of civilians wielding their own guns, attempting to return fire."

Giffords, whose ability to speak has been limited since the shooting, told her former colleagues, "The nation's counting on you."

Democrats wondered, however, whether the Las Vegas attack would change any minds on Capitol Hill. Rep. Jamie B. Raskin (D-Md.) said he hoped the scale of the tragedy, with many dozens dead and hundreds wounded, would make a difference.

"Those hundreds of people and their thousands of family members and friends are not going to let this go," he said.

Another lawmaker who spoke out Monday is Sen. Chris Murphy (D-Conn.), who sought to tighten gun laws in the aftermath of the 2013 mass shooting in Newtown, Conn., that left 20 children and five adults dead at Sandy Hook Elementary School.

Legislation that would have expanded the use of federal background checks failed in the Senate five months after the Newtown killings.

"It is positively infuriating that my colleagues in Congress are so afraid of the gun industry that they pretend there aren't public policy responses to this epidemic," Murphy said. "There are, and the thoughts and prayers of politicians are cruelly hollow if they are paired with continued legislative indifference. It's time for Congress to get off its ass and do something."

Gun-control advocates zeroed in — not on the type of guns used but on laws that could change how the shooter got them.

Kris Brown and Avery Gardiner, co-presidents of the Brady Center to Prevent Gun Violence, said in an interview that Congress should again try to close loopholes in the national background-check law. People can avoid a background check if they buy a gun online, in a private sale or at a gun show.

Federal law also allows a gun sale to go through if a background check is not completed in three days — a factor in how Dylann Roof obtained a gun in the 2016 church massacre in Charleston, S.C. The result, Brown and Gardiner said, is that an estimated 1 in 5 guns sold in this country avoids a background check.

"I think it's a mistake when people focus on the difference between a semiautomatic weapon and a fully automatic weapon," Gardiner said. "They are weapons of mass destruction. What we need now is a federal system so we're not left with a patchwork of laws across the country."

Amber Phillips contributed to this report.

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