Sen. Chris Murphy (D-Conn.), who led a 15-hour filibuster this week, spoke at a press conference on gun-control legislation on June 16 on Capitol Hill. (Win Mcnamee/Getty Images)

An effort to pass new gun-control legislation in the wake of a deadly mass shooting in Orlando is poised to end in a familiar impasse in the coming days — and potentially pit Republican lawmakers against their presumed presidential nominee, Donald Trump, who called for congressional action.

The long-contentious issue quickly gripped Capitol Hill anew this week after a shooter killed 49 people at a nightclub early Sunday in Orlando. The 29-year-old assailant had been on the FBI’s terrorist watch list, but he was removed in 2014 because of a lack of evidence that he would commit an immediate crime.

Trump said this week that lawmakers should find a way to bar terrorism suspects from obtaining guns and that he planned to meet with the nation’s top gun lobby to build support. At the same time, some Republicans and Democrats jumped at the chance to renew their efforts to reach compromise. But the effort didn’t go far.

Gun rights advocates in Congress quickly made clear that they were unlikely to be swayed by Trump’s decision to jump into the debate.

“There’s nothing wrong with him trying to energize the discussion on it and work out something that would be healthy and that we can all agree on. I think that’s positive,” said Sen. Jeff Sessions (R-Ala.), one of Trump’s earliest supporters on Capitol Hill.

The Fix's Amber Phillips breaks down why Congress is unlikely to pass major gun control legislation, despite Sen. Chris Murphy (D-Conn.) filibustering for 15 hours on June 15. (Peter Stevenson/The Washington Post)

But Sessions said that gun control is “not the greatest issue in the world” and that congressional Republicans shouldn’t take cues from Trump on the subject.

“We’re a co-equal branch of government,” he said.

Additionally, several delegates to the Republican convention in Cleveland next month warned that they would take steps to bolster the party platform’s language on Second Amendment rights if legislation passed the Senate. Some delegates said this week that they might withhold support for Trump at the convention if he continued to call for new laws.

Wendy Day, a GOP convention delegate from Michigan, said that many of her party colleagues were startled to see Trump “turn left when it came to the Second Amendment. I think that surprised and angered a lot of people.”

Democrats have long wanted to prevent terrorism suspects from acquiring guns or explosives and to impose mandatory background checks for firearms sold at gun shows and through online dealers. Republicans have offered bills that would keep guns away from terrorism suspects, but only if authorities can prove probable cause within three business days of the attempted sale.

To jump-start action on the issue, Democrats launched a nearly 15-hour Senate filibuster on Wednesday that concluded early Thursday. Hours later, leaders from each party announced plans to hold votes Monday on a series of bills.

But the four measures — two from Democrats, two from Republicans — have all been rejected in the past and are expected to fail again this time, highlighting the continuing divide between Democratic and Republican senators on guns.

[Why it makes perfect sense that Chris Murphy is leading a gun-control filibuster]

Signs that lawmakers would retreat to their usual party positions in Monday’s planned votes prompted complaints that both parties had rushed to politicize the mass killing.

Sen. Charles E. Schumer (D-N.Y.) dismissed the GOP proposals as “a way for them to say they’re doing something when they are doing nothing.”

Sen. Bob Corker (R-Tenn.) lamented, “Instead of trying to find a solution that would work and still protect people’s constitutional rights, we’re going to battle to a draw on Monday night.”

Senate Majority Leader Mitch McConnell (R-Ky.) slammed Democrats for using the Senate floor as a “campaign studio” to score political points. He faulted several Democrats for skipping a closed-door briefing led by top national security officials on Wednesday so that they could continue their “talk-a-thon.”

“It’s hard to think of a clearer contrast for serious work for solutions on the one hand, and endless partisan campaign on the other,” McConnell said Thursday.

Trump’s decision to jump into the gun-control debate, long an emotionally fraught issue in Washington, further clouded the atmosphere. He has neither detailed how Congress should proceed nor scheduled his meeting with the National Rifle Association. Even Trump’s strongest congressional allies — all ardent gun rights advocates — struggled to explain his position.

Some GOP senators declined altogether to discuss Trump’s remarks, claiming they were too focused on the gun-control votes at hand.

“Members who want to be legislators are actually looking for solutions,” said Sen. Roger Wicker (R-Miss.), who is in charge of the Senate GOP’s 2016 election operation.

Even if senators pass a gun bill, it’s unclear how the legislation would be received in

the more conservative House. Speaker Paul D. Ryan (R-Wis.) on Thursday told reporters: “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.”

Plans for the series of votes were announced as President Obama, Vice President Biden and a gaggle of Florida lawmakers including Sen. Marco Rubio (R) traveled to Orlando to meet with the families of shooting victims and survivors of the massacre. After placing a bouquet of white roses among the balloons and other flowers at a makeshift memorial at a downtown arena, Obama urged lawmakers to act.

“I truly hope that senators rise to the moment and do the right thing. We can stop some tragedies. We can save some lives,” Obama said. “If we don’t act, we will keep seeing more massacres like this.”

Sen. Christopher Murphy (D-Conn.), who led the Senate filibuster, marveled Thursday that his decision to hold the Senate floor had pressured Republican leaders to commit to holding the votes.

“We still have to get from here to there, but we did not have that commitment when we started,” he said early Thursday. But he added that there was “no guarantee that those amendments pass.”

Mike DeBonis contributed to this report.