But he never tires of the many people who approach him, sometimes quietly, with praise for his support for tightening restrictions on gun buyers, voters “who recognize it was a politically difficult thing to do,” he said.
Mr. Toomey, a conservative Republican in a tough re-election fight in Pennsylvania, has been rewarded with support from unlikely sources: former Representative Gabrielle Giffords of Arizona, a Democrat who was shot in the head in a 2011 assassination attempt and started a political action committee focused on gun control, and Michael R. Bloomberg, a former mayor of New York, who is behind another gun control PAC.
But the two are also backing Gov. Maggie Hassan of New Hampshire, the Democratic challenger to Senator Kelly Ayotte, a Republican who has opposed the legislation that bears Mr. Toomey’s name. Ms. Hassan and Ms. Ayotte are locked in one of the tightest Senate races in the country.
The split illustrates a new dimension in the gun control debate in Senate races after the issue largely went underground over the past decade as candidates tried to avoid talking about it.
Emboldened by a horrified reaction to recent mass shootings and growing support among suburban voters for modest gun control steps, groups that back new laws are inserting themselves into the 2016 races, with party politics at times taking a rare back seat.
Both groups also have endorsed Senator Mark S. Kirk, Republican of Illinois, over his Democratic challenger, Representative Tammy Duckworth.
“This is an issue everyone thought was the third rail in federal campaigns,” said John Feinblatt, the president of Everytown for Gun Safety, an organization aligned with Mr. Bloomberg. “We are going to support people who have shown courage on this issue.”
In Nevada, a PAC directed by Democrats has run ads in Las Vegas and Reno criticizing Representative Joe Heck, a Republican running against Catherine Cortez Masto for the seat of Senator Harry Reid, who is retiring. Mr. Heck voted against measures aimed at preventing those on terror watch lists from obtaining guns.
In Florida, Mr. Bloomberg’s PAC, Independence USA, ran television ads in support of the successful House Democratic primary candidacy of Val Demings, a former Orlando police chief.
Ted Strickland, the former Democratic governor of Ohio who is trying to unseat Senator Rob Portman, a Republican, once was a fierce defender of gun rights but is now attacking the National Rifle Association. The group has responded by spending close to $2 million to try to defeat Mr. Strickland.
In Florida, the scene of the Pulse nightclub massacre, Representative Patrick Murphy, a Democrat, is using the issue in his Senate campaign against Marco Rubio, the incumbent Republican, noting that Mr. Rubio was endorsed by the N.R.A. soon after the shooting.
But nowhere is the issue being pushed more than in New Hampshire and Pennsylvania. Ms. Giffords’s group, Americans for Responsible Solutions, has spent nearly $1.5 million hammering Ms. Ayotte on her record, which has left the incumbent moving quickly to support legislation aimed at preventing gun purchases for those on terror watch lists.
Ms. Giffords has endorsed Mr. Toomey, who after the Sandy Hook school massacre sponsored legislation with Senator Joe Manchin III, Democrat of West Virginia, to stiffen laws on background checks of gun buyers.
The measure failed, but Mr. Toomey, who is trailing slightly in his race against Katie McGinty, a Democrat, has highlighted Ms. Giffords’s endorsement, something of a lifeline to him in the suburbs of Philadelphia and Pittsburgh.
“The goal writ large is to make it clear we stand by our friends and allies and help them get re-elected even when they are Republicans,” said Howard Wolfson, Mr. Bloomberg’s political adviser, and, as in the case of Ms. Ayotte, to “help defeat people who took a bad vote and didn’t stand up.”
Mr. Bloomberg’s group has run ads supporting Mr. Toomey and Ms. Hassan, and it plans to spend more than $10 million before Election Day to support both candidates. “There is just the compelling logic that as a society, there is a category of people we do not want to own firearms,” Mr. Toomey said.
Ms. Ayotte has scrambled to show that she supports some strengthening of background checks, noting often that she had voted for a Republican measure that had sought to improve the way the system links to mental health records.
She also recently voted for two competing bills — one offered by Democrats, the other by Republicans — aimed at preventing terrorists from obtaining guns, and worked with Senator Susan Collins, Republican of Maine, on a compromise measure that never came to a vote.
The Democrats who are targeting Mr. Heck in Nevada on guns are racing to support Ms. McGinty in ads that point out Mr. Toomey has voted against many other gun control bills.
“Katie’s positions on gun safety, unlike Pat Toomey’s, have been consistent,” said Sean Coit, a spokesman for the campaign, noting that Ms. McGinty had been endorsed by CeaseFire Pennsylvania, a gun safety organization.
How much the issue resonates in the two states is unclear. “It is, certainly in the Philly suburbs and the Lehigh Valley,” said G. Terry Madonna, the director of the Center for Politics and Public Affairs at Franklin & Marshall College in Lancaster, Pa. “But it is not an issue driving voter behavior.”
Groups like the N.R.A. and the National Shooting Sports Foundation are countering with their own ads for candidates like Mr. Heck.
“We encourage hunters, target shooters, sportsmen and women and gun owners to register to vote, and then, on Election Day, armed with the facts, to vote for the candidates they think will do the best job protecting their rights,” said Mike Bazinet, a spokesman for the shooting sports foundation. He declined to say how many states the group would advertise in or how much money it would spend.
But gun control groups, spurred mostly by Democrats, are reinvigorated after years of more tepid efforts. President Obama — whose 2008 campaign was largely silent on guns — now says he will not back candidates who do not support new regulations. Hillary Clinton used the issue in the Democratic presidential primary race to beat back Senator Bernie Sanders of Vermont, who has had a mixed voting record on gun matters.
This year, Senate Democrats staged a filibuster over guns, and House Democrats conducted an overnight sit-in on the House floor. Since Sandy Hook, it has been increasingly hard for Democrats who support gun rights to advance in primaries.
“I don’t know if guns was even mentioned at the 2008 convention,” said Pia Carusone, a senior adviser with Ms. Giffords’s group. “Now the issue has taken a seat at the table with choice and climate change and marriage equality.”
This Article originally appeared in The New York Times