US Democrats claimed victory Thursday after a nearly 15-hour filibuster persuaded the Senate to vote on legislation barring terror suspects from buying firearms, as Donald Trump signalled he could modulate his gun rights stance and back such a move.
The breakthrough in the Republican-controlled Senate, potentially ending a years-long logjam on how to reduce US gun violence, follows the weekend massacre of 49 people at a gay nightclub in Orlando, Florida.
It was the deadliest mass shooting in US history.
Democrats and some Republicans have joined in questioning how a man investigated for suspected extremist ties and who previously figured on an FBI watchlist was able to commit mass murder with a legally purchased assault rifle.
Under so-called "no-fly no buy" legislation, people on US terror watchlists or no-fly lists would be barred from acquiring firearms.
The filibuster, a procedural obstruction, was led by Senator Chris Murphy of Connecticut, where the Sandy Hook shooting left 26 people dead in 2012, most of them elementary school children.
"I'm at my wit's end," said Murphy, as he began his takeover of the Senate floor.
"I'm going to remain on this floor until we get some signal, some sign that we can come together."
Murphy, with support from 40 senators including Republican Senator Pat Toomey, spent hours discussing ways to reduce gun violence -- a tactic that eventually prompted leaders to schedule a vote on gun measures.
At 1:53 am (0553 GMT) Thursday, he claimed victory on Twitter.
"I am proud to announce that after 14+ hours on the floor, we will have a vote on closing the terror gap & universal background checks" including for sales at gun shows and on the Internet, Murphy wrote.
Passage of such controversial measures, particularly the background check expansion, is unlikely in the toxic 2016 election climate.
Republicans largely oppose legislation that would deny weapons to people on such lists, arguing it would infringe on the Second Amendment rights of everyday Americans, including those who may have been placed unfairly on suspect lists.
Studies however show a large majority of Americans support such limits.
Murphy told MSNBC he and fellow Democrats will pressure Republicans to consider the "no-fly no buy" legislation and insisted "we have a shot to at least get that passed."
Republican House Speaker Paul Ryan however poured cold water on the prospect of swift action.
"We don't take away citizens' rights without due process," Ryan told reporters.
"And so if you have a quick idea in the heat of the moment that says let's take away a person's rights without their due process, we're going to stand up and defend the constitution."
Trump, the presumptive Republican presidential nominee, made waves Wednesday when he tweeted that he would meet with the National Rifle Association "about not allowing people on the terrorist watchlist, or the no fly list, to buy guns."
The softening of his stance may put Trump on a collision course with the powerful NRA, which has said that restrictions "like bans on gun purchases by people on 'watchlists' are ineffective, unconstitutional or both."
The group answered that they would be "happy to meet" with the Republican flagbearer.
"The NRA believes that terrorists should not be allowed to purchase or possess firearms, period," the group said in a statement.
"Anyone on a terror watch list who tries to buy a gun should be thoroughly investigated by the FBI and the sale delayed while the investigation is ongoing."
Republican Senator Lindsey Graham, who has clashed with Trump, told Fox News that this time, he was "on the right path... when it comes to making sure guns don't fall into the hands of people who can't fly on airplanes."
Trump's Democratic presidential rival Hillary Clinton supports the limits pushed by Murphy.
"Surely we can agree, if the FBI is watching you for suspected terrorist links, you should not be able to buy a gun with no questions asked," she said.
The renewed push for legislation comes after a US government report showed that known terror suspects have passed background checks for gun sales 91 percent of the time since 2004.
"I do think our filibuster made a difference," Murphy told CBS This Morning.
"Let's be honest. The Senate was not going to debate these measures, had no plans to talk about ending gun violence this week on the floor of the Senate."
A measure that would have stopped those on FBI watchlists from buying firearms and explosives failed in December, with every Senate Republican but one voting in opposition.
Some Republicans appear to be reconsidering, including congressman Bob Dold, who is facing a tough re-election fight in Illinois.
"Thoughts and prayers are not enough," Dold said Tuesday on the House floor.
"It's time for action."