For nearly a decade, Sen. Pat Toomey (R., Pa.) has been at the center of Congress’ frequent debates on gun laws, one of the few Republicans willing to support some efforts to tighten the rules.

Now, after the latest round of horrific massacres, Toomey says a group of senators are closer than he’s ever seen to a bipartisan agreement. He told Fox News Monday that he hopes negotiators can develop a framework by the end of this week, though he indicated that timeline could be a stretch.

“I certainly can’t guarantee any outcome, but it feels to me like we are closer than we have been since I have been in the Senate,” Toomey said a day earlier on CBS’s Face the Nation.

But what form any agreement takes, and how far it goes, is unclear. It’s sure to fall well short of what President Joe Biden and gun control advocates have called for, and likely won’t go as far as Toomey’s 2013 bill with Sen. Joe Manchin (D., W. Va.), which would have expanded background checks to cover all commercial gun sales.

Toomey proposed that plan in the aftermath of the Sandy Hook school shooting in Connecticut, but after its failure, many in Washington worried nothing could bring about tougher gun laws. The latest spate of massacres, including one that killed three in Philadelphia on Saturday, has prompted a new round of urgency, but with still deeply uncertain prospects of anything becoming law.

To win bipartisan support, the ideas now under discussion are more limited than in some past pushes. They include some expansion of background checks, federal incentives to encourage states to adopt red flag laws, ideas to make schools more secure, and passing a federal law against gun trafficking. (Red flag laws allow authorities to remove a person’s firearms if they are deemed to be a threat to themselves or others.)

Other proposals long-sought by Democrats and Biden, such as a ban on so-called assault weapons and high-capacity magazines, still appear far short of the 60 votes required to pass the Senate in the face of opposition from Republicans and, on some proposals, possibly a few Democrats.

“My hope is we’ll get at least half the Republican conference” to back some of the more modest proposals, Toomey said Sunday. “That should be the goal here. We’re going to have to be realistic about what can do that. … It’s not going to be everything, certainly, that Democrats would like.”

Toomey’s role in the talks highlights one of the major potential consequences of the ongoing campaign to succeed him, after Toomey declined to seek reelection this fall. GOP nominee Mehmet Oz has written that he opposes red flag laws, universal background checks, and “any gun-control measure that infringes upon the Second Amendment.” The Democratic nominee, Lt. Gov. John Fetterman, by contrast, would vote for all of those ideas, as well as bans on assault weapons. Either candidate would alter the balance of votes in the closely divided Senate.

Toomey, who has a staunchly conservative voting record on most issues, said the latest discussions include a number of Republicans who haven’t been engaged on gun laws in the past, giving him hope that this time can be different, even with a Senate that’s more conservative than the one that blocked his background-check bill in 2013.

Frustration over gun violence

This is Toomey’s chance “to prove his word,” said Adam Garber, executive director of CeaseFire PA, which advocates for tougher gun laws.

”For years, he has said he wants to find reasonable solutions to this crisis,” Garber said Monday. “This is his last chance to fulfill what he’s said again and again.”

Frustrations are running high, both among violence-prevention advocates and the communities most affected by Philadelphia’s ongoing shootings crisis, he said. While his group supports even incremental changes, the potential compromise legislation should be considered a first step, he argued.

“The public is going to recognize that if the bloodshed continues, it means they didn’t go far enough,” Garber said.

Sen. Bob Casey (D., Pa.), who once opposed new gun laws but changed his position after Sandy Hook, argued that a bill to expand background checks, increase funding for mental health resources, and make it harder for people considered an “extreme risk” to obtain a weapon ”would be significant,” even if he would prefer to go much further.

“Now’s the time to make progress,” Casey said as he met in Philadelphia Monday with a dozen young people in a roundtable discussion about the city’s gun violence crisis.

» READ MORE: From 2013: Toomey: 'I gave this my best shot'

George Lane, who attended, described how he was just 2 when his older brother was fatally shot. Now 15, Lane said he’s turning his “pain into passion” and is part of a group of students pushing for stronger gun laws and asking elected officials to engage with the people most affected.

”Change to me is being able to move freely throughout the whole city without wondering if you’re going to make it home alive,” he said.

Cayla Waddington, a 15-year-old who’s in a coalition of Philadelphia teens trying to prevent shootings, said her group surveyed 1,300 fellow students and found that most think “better gun laws” are the clearest solution.

“If you ask our Founding Fathers from the 1700s about an assault rifle, they would be like, ‘What is this?’ Their weapons took 20 minutes to reload,” she said.

Proposals wouldn’t stop shootings, gun rights groups say

Advocates for gun owners argue that the ideas under discussion would do little to stop mass shootings.

“All of this talk about what they’re proposing is only going to manifest itself in impact on law-abiding citizens,” said Kim Stolfer, president of the lobbying arm of the Pennsylvania-based Firearms Owners Against Crime.

He blamed mass shooting on lax law enforcement, saying that even states with tough gun laws have seen mass shootings. “I’d like to bring some sanity to the equation, if you will, and have them focus, or refocus on why these things happen in the first place,” Stolfer said.

» READ MORE: U.S. Sen. Bob Casey after South Street shooting: Police ‘can’t solve this on their own’

Toomey has acknowledged that even the ideas he supports wouldn’t have stopped some of the mass shootings that have prompted the latest efforts in Congress.

“A determined criminal is going to be able to eventually get a gun, I understand that,” Toomey told Fox News Monday. “But that doesn’t mean there’s nothing we can do to make it harder for that person to get a gun.”

Despite polling showing widespread support for universal background checks, Toomey’s own careful positioning on gun laws in a 50-50 Senate illustrates why it has been so hard to pass anything that tightens the rules around firearms purchases, especially with 60 votes required for approval.

Toomey supports expanding background checks as a way to hinder people from buying guns who legally aren’t allowed to, such as those with violent criminal records or dangerous mental illness. He has signaled openness to red flag laws, while saying any such law needs ample due process for gun owners.

But Toomey opposes other plans, such as banning assault weapons and high-capacity magazines, that would also apply to law-abiding citizens and that he sees as infringing on constitutional rights.

With Toomey retiring, the Senate’s effort this month could be the last chance for gun control advocates to count on support from both of Pennsylvania senators’ for at least some measures.

Staff writer Julia Terruso contributed to this article.