Sen. Mark Kirk said he won't support Donald Trump or Hillary Clinton in the general election. | AP Photo Giffords' anti-gun violence PAC endorses Toomey, Kirk

Americans for Responsible Solutions, the anti-gun violence PAC founded by former congresswoman Gabby Giffords and her husband, Mark Kelly, on Monday endorsed two Republican senators for their 2013 vote following the Sandy Hook Elementary massacre.

"In the wake of the tragedy at Sandy Hook, Republican Sens. Pat Toomey and Mark Kirk broke from the gun lobby and supported a bill to help prevent felons, domestic abusers and the dangerously mentally ill from obtaining firearms at gun shows and online," Giffords and Kelly wrote in a CNN op-ed. "This week, they are earning our organization's endorsement."


Both incumbent Republicans face difficult paths to reelection in November, with Pennsylvania's Toomey narrowly trailing Democratic challenger Katie McGinty in the latest Quinnipiac University poll. Illinois Sen. Kirk is perhaps even more endangered, facing a strong challenge from Democratic Rep. Tammy Duckworth and openly disavowing GOP presidential nominee Donald Trump. Arizona Sen. John McCain, along with Maine Sen. Susan Collins, also voted in favor of the legislation. But the group is not endorsing McCain, who is the only other Republican who voted for the bill up for reelection.

Giffords and Kelly called out New Hampshire Sen. Kelly Ayotte for voting against background check loopholes after the Newtown, Connecticut, shooting in 2013 and subsequently signaling that she supports measures focused on strengthening background checks.

"No matter: Our organization has run advertising highlighting her vote and her deception," they wrote. "Now, polls have swung against her."

The group is also endorsing Sen. Michael Bennet (D-Colo.), who is running significantly ahead of Republican challenger Darryl Glenn in the polls, while acknowledging that their endorsement of the two Republican senators was not an easy decision to make.

"In Pennsylvania, Katie McGinty is a passionate advocate for gun violence prevention and would be a consistent vote for life-saving gun safety laws in the Senate," they wrote. "Likewise, Tammy Duckworth of Illinois is not only a decorated veteran and an American hero, but has been a champion for commonsense gun laws in the House. We have no doubt she would continue to be a leader on gun safety in the Senate."

The Pennsylvania Democratic Party registered its disapproval of the endorsement.

“Pat Toomey isn't a moderate on guns, period,” party spokesman Preston Maddock said. “He's stood in the way of common sense gun safety laws and he would happily keep Mitch McConnell as the Senate Majority Leader, meaning that gun safety laws have almost no chance in the Senate.”

Seung Min Kim contributed reporting.