WASHINGTON - The debate on gun laws roiled national politics Wednesday, with Donald Trump suggesting that he might be open to a plan to bar suspected terrorists from buying firearms, Sen. Pat Toomey (R., Pa.) offering a plan to do just that, and Sen. Cory A. Booker of New Jersey helping lead a marathon Democratic push on the Senate floor demanding action.

But amid a heated political season, a day that began with talk of compromise ended with signs that the Orlando shooting would wind up producing the same intractable and emotional divides that have characterized Congress' responses to previous massacres.

Trump and some Republicans had opened the door to a different result by expressing openness to the notion, advanced by Democrats, to ban gun purchases by anyone on government terror watch lists. Key lawmakers in both parties were in talks about a plan to accomplish that while protecting the rights of people who might be listed in error.

Separately, Toomey, long a key figure in the gun debate, announced he would introduce his own plan Thursday to address that issue.

"It's time to get something done here," Toomey said 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."

But shortly after Toomey introduced his plan, Democrats dismissed it and continued to push their own version without Republican support.

And in another sign that deals on the charged issue remain elusive, talks between Toomey and a group founded by former New York Mayor Michael Bloomberg, a gun-control advocate, failed to produce unity.

"While we are encouraged that there have been some discussions, we are not there yet, and our support for any compromise legislation is contingent on support from both Republicans and Democrats," said a spokeswoman for the group, Everytown for Gun Safety.

A Toomey spokeswoman said he was still working to line up bipartisan support.

But the Senate's top Democrat, Harry Reid of Nevada, accused Republicans of engaging in sham negotiations, and said Toomey's plan would be too onerous on law enforcement, moving the parties "farther away from compromise, not closer."

Toomey's Democratic challenger this fall dismissed his proposal as an election-year stunt designed to give the appearance of action without producing results.

"Sen. Toomey is making a political calculation, not a principled stand," said Sean Coit, a spokesman for Democrat Katie McGinty.

The two are competing in one of the country's most critical races, with Toomey's history of supporting some new gun laws a key point of contention in a contest that could decide control of the Senate.

His announcement came hours after Democrats took control of the Senate floor, holding it throughout the day to demand votes on bills to expand background checks and close the so-called terror gap that allows people on federal watch lists to pass background checks to buy guns.

"I've cleared my entire day. This will not be business as usual," Booker said in an impassioned speech around noon, aiding an effort led by Sen. Chris Murphy of Connecticut. The two remained on the floor well into the night.

In recent days, Trump and some Senate Republicans said they were open to the idea of tightening rules that could cut off gun buys by suspected terrorists. Trump, the presumptive Republican presidential nominee, wrote Wednesday on Twitter that he would discuss the idea with the NRA.

The gun owners' group sent mixed signals on whether it would support the idea.

"We are happy to meet with Donald Trump. The NRA's position on this issue has not changed. The NRA believes that terrorists should not be allowed to purchase or possess firearms, period," said a statement from Chris Cox, head of the group's political arm. "At the same time, due process protections should be put in place that allow law-abiding Americans who are wrongly put on a watch list to be removed."

The parties have clashed over how to balance strong oversight with an appeals process for people who might be mistakenly added to a watch list.

The issue carries particular political weight for Toomey.

In the aftermath of the 2012 shooting at a Newtown, Conn., school in which 20 children and six adults were killed, Toomey stood as the lead Republican on a bill to expand background checks for gun purchases - one of the only GOP lawmakers to support the idea. While the bill fell short, Toomey won praise and the push became a key part of his reelection campaign.

Democrats, however, have tried for days to undercut his standing by pointing to his vote last year against an earlier Democratic plan to stop people on terror watch lists from buying guns.

Toomey said he opposed that bill because it did not allow people placed on the lists enough opportunity to challenge those decisions. He backed 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.

On Wednesday, he was the second Republican to join Democrats' lengthy floor discussion, and later proposed a plan that he said would represent a compromise.

It would require the U.S. attorney general to create a list of suspected terrorists who would be barred from gun purchases. The list 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.

He planned to formally introduce the plan Thursday.

Booker and other Democrats, meanwhile, called for action from the Senate floor.

"This violence in our country will continue unless we take measures, commonsense measures, to restrict these firearms going to known or suspected terrorists," Booker said.

Sens. Robert P. Casey Jr. (D., Pa.) and Bob Menendez (D., N.J.) also took turns to speak.

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

Both parties seemed to want to change that dynamic. Whether they can agree on a solution remained as unclear as ever.

jtamari@phillynews.com @JonathanTamari www.philly.com/capitolinq