The Las Vegas massacre could be the event that gets Congress to pass the first gun control legislation in a generation. But it will depend on President Trump.

After the Sunday-night shooting that left 58 dead and about 500 injured, several leaders in the Republican-led Congress are showing new openness to legislation that would regulate bump stocks, the devices used by the Vegas shooter to make his semi-automatic rifles fire like automatics. Audio analysis suggests he sprayed the crowd at the Route 91 Harvest country music festival with 280 rounds in just a 31-second stretch of the attack, which went on for 11 minutes.

Republicans are usually united in opposition to any gun control, but this mass shooting, the deadliest in modern U.S. history, has turned “no” into “maybe,” “could be,” “possible,” and “needs further study.”

House Speaker Paul Ryan told MSNBC host Hugh Hewitt in an interview that bump stocks are “something we need to look into.” John Cornyn echoed that: “It seems like it’s an obvious area we ought to explore and see if it’s something Congress needs to act on,” the Texas senator, the second-highest-ranking Republican who earned an A+ rating from the National Rifle Association in his last election, told the New York Times. “I don’t understand the use of this bump stock.”

And the Senate’s third-highest-ranking Republican, Sen. John Thune of South Dakota, also expressed openness, telling Politico, “I think it’s something we ought to look into.” In the immediate aftermath of the shooting, Thune had struck a far more defeatist tone, telling NBC News: “I think people are going to have to take steps in their own lives to take precautions.”

“As somebody said: ‘Get low,’” he had added.

Several Republican House members — some from very conservative states like Oklahoma and Kansas — went even further and said they would support a bump stock ban to be introduced Thursday by Republican Rep. Carlos Curbelo of Florida and Democratic Rep. Seth Moulton of Massachusetts. California Democrat Sen. Dianne Feinstein has also proposed a bill to ban bump stocks.

But the sudden receptiveness among GOP members doesn’t mean there will be fast action, or any action.

Trump would almost certainly need to embrace the legislation in order for Republicans to rally behind it. “Trump needs to take the lead on this bump stock issue. He’s the only one that can,” Rep. Tom Rooney of Florida, the House Majority Deputy Whip, told Politico Playbook. Many Republicans ran for Congress promising to protect Second Amendment rights and there be a tremendous backlash from constituents and the NRA to supporting a gun control bill, even one as modest as a bump stock ban.

Trump’s views on the bump stock ban are not yet known. Asked about gun control earlier this week, Trump told reporters, “We’ll talk about gun laws as time goes on.”

Trump’s decision may also depend on the NRA’s reaction. The gun lobbying group spent over $30 million to help Trump win last year’s presidential election, the most they have ever spent on a presidential election and the most spent on behalf of Trump by any outside group, including his own super PAC.

The NRA has so far been silent following the shooting in Vegas and have not commented on a bump stock ban. Their top legislative priority, the SHARE Act which rolls back gun controls, is also on the verge of passing the House of Representatives. They are normally opposed to all forms of gun control.