WASHINGTON – In a potential shift in the debates on gun laws, Donald Trump and some Senate Republicans are now saying they would consider new laws to limit suspected terrorists' ability to buy guns – opening a door to action that has long eluded advocates for tougher restrictions on firearms purchases.

Sen. Pat Toomey (R., Pa.), a key figure in the contentious argument, renewed his advocacy Wednesday, taking part in a Democratic takeover of the Senate floor and later saying he would introduce a bill Thursday to bar anyone on a federal terrorist watch list from buying guns, but also creating an annual review of the names on that list. He was hoping for support from a group founded by gun control advocate and former New York Mayor Michael Bloomberg, his office said, though sources familiar with those talks said the organization had balked at some of Toomey's plans, finding them too onerous on federal authorities monitoring suspected terrorists.

"It's time to get something done here," Toomey said earlier on the Senate floor. "Everybody ought to be in agreement in principle: we don't want terrorists to be able to walk into a gun store and buy a gun, and we don't want an innocent, law-abiding citizen to be denied second amendment rights because he's wrongly on the list with a bunch of terrorists. This is not rocket science to figure this out."

Toomey was just the second Republican to join the Democrats' quasi-filibuster, in which they took control of the Senate floor around 11:30 a.m. and for hours demanded votes to expand background checks for gun purchases and ban buys by suspected terrorists.

"I've cleared my entire day. This will not be business as usual. I've cleared my evening events," Sen. Cory Booker (D., N.J.) said in an impassioned speech, aiding an effort led by Sen. Chris Murphy (D., Conn.), who has talked relentlessly about gun violence ever since 20 children and six teachers were killed in an elementary school massacre in his home state.

As of 6 p.m. Booker had spent nearly seven hours on the Senate floor, joining Murphy.

Toomey, who sponsored a background check bill after Newtown, said his plan would address the so-called "terror gap" that allows people on federal terrorism watch lists to buy guns. He had discussions with Bloomberg's Everytown for Gun Safety, according to a spokeswoman for the organization, but there were conflicting reports about whether the group would endorse Toomey's final proposal.

A Toomey spokeswoman said the group agreed to support his measure if he found bipartisan support. The group did not immediately respond to a request for confirmation.

It also wasn't clear if Toomey's proposal would get a vote. Other Democrats and Republicans were said to also be working on a compromise.

The developments suggest that unlike past shootings, the Orlando massacre last week has a chance to spur some legislative compromise on gun laws -- though recent history is also littered with pushes for new laws that began with emotional appeals, and ended in defeat.

This time, however, the incident has thrust the gun debate into the midst of a heated election season, one in which Democrats have made a top priority of unseating Toomey and other vulnerable Republicans as they try to take control of the Senate.

While most in the GOP oppose most new gun laws, in recent days Trump and some other Senate Republicans said they were open to the idea of tightening rules that could cut off purchases by suspected terrorists.  Trump, the presumptive Republican presidential nominee, wrote on Twitter Wednesday that he would discuss the idea with the NRA.

Toomey's plan, he said, would allow the U.S. attorney general to block sales of guns to suspected terrorists. But -- responding to concerns that ordinary gun buyers might be wrongly included on watcch lists -- his plan would require the attorney general to create a list of likely terrorists that would need approval and annual review by the Foreign Intelligence Surveillance Court. His measure would also require the attorney general to turn over evidence to anyone on the list who challenges a decision to stop a gun purchase.

Toomey was at the center of the most recent sustained push for new gun laws. In the aftermath of the Sandy Hook shooting he stood as the lead Republican on a bill to expand background checks for gun purchases. While the bill fell short, Toomey won widespread praise and the push became a key part of his reelection campaign.

In the days since the massacre, however, Democrats have attacked Toomey for not doing enough to push that bill and for opposing an earlier Democratic plan to stop people on terror watch lists from buying guns.

"It's only now, when his political future is in jeopardy from bad headlines and mounting criticism that he will even consider how we can make it harder for potential terrorists to buy guns," said Sean Coit, a spokesman for Democratic challenger Katie McGinty. "Sen. Toomey is making a political calculation, not a principled stand."

Toomey has said he opposed the Democratic anti-terror bill because it did not allow people placed on the lists enough opportunity to challenge those decisions. He instead supported a Republican version that put the burden of proof on the government, giving authorities three days to show probable cause to stop gun sales to suspected terrorists. Democrats derided that plan as too weak, and easily evaded.

On Wednesday, though Toomey agreed that the GOP bill did not give authorities enough muscle, and said he was trying to find a middle ground.

Booker, meanwhile, joined the Democratic effort to highlight the issue with a lengthy discussion on the Senate foor.

"We must stand because this violence in our country will continue unless we take measures, common sense measures, to restrict these firearms going to known or suspected terrorists," Booker said.

Working in the background as Murphy led the Democratic effort, Booker stayed on the Senate floor and helped direct colleagues who arrived to help.

Sens. Bob Casey (D., Pa.) and Robert Menendez (D., N.J.) later joined as well.

"Why is it if you're too dangerous to be on an airplane, you're not too dangerous to have a weapon?" Casey asked.

You can follow Tamari on Twitter or email him at jtamari@phillynews.com.