A gun-safety group founded by former U.S. Rep. Gabby Giffords endorsed Sen. Pat Toomey (R., Pa.) Monday, adding to a growing list of gun-control supporters backing the incumbent.

The political action committee, Americans for Responsible Solutions, said it hopes to line up more support for its cause among congressional Republicans like Toomey. At the same time, its backing could help the incumbent, locked in an ever-closer race with Democrat Katie McGinty, attract moderate voters.

Giffords and her husband, astronaut Mark Kelly, announced the endorsement in an opinion piece written for CNN - but said their decision in Pennsylvania was difficult. They called McGinty "a passionate advocate for gun violence prevention" who would be "a consistent vote for life-saving gun safety laws."

Giffords, a Democrat and former Arizona congresswoman, was one of 18 people shot by a mentally disturbed gunman at a Tucson political event in 2011. Six died and a dozen were injured, and the incident led to renewed calls for more stringent gun-control measures.

Toomey, who introduced a background-check bill with Sen. Joe Manchin (D., W. Va.) after the December 2012 shooting at Sandy Hook Elementary School, has won praise over the years from Democrats, including President Obama, for bipartisan work on gun-control. The bill failed to advance by six votes.

"I have long said that we must work together to forge a bipartisan consensus on gun safety, rather than talk past one another with partisan rhetoric," Toomey said in a statement Monday.

This summer, Toomey urged compromise on a bill to ban terror suspects from buying guns after the June massacre in Orlando. But in December and June, he also opposed Democratic efforts. He voted against a broader Democratic background-check bill in June.

McGinty on Monday hammered her opponent for voting against the terror loophole measures.

Responding to a question about the endorsement while speaking at the Pennsylvania Press Club in Harrisburg, McGinty said Toomey "has not been a leader" on gun safety. "After tragedies like San Bernardino, like Orlando, the senator was literally begged to reintroduce his legislation and refused, saying, 'Let's let the Democrats take the lead,' " she said.

For Toomey, the Giffords backing is the latest dose of support that his campaign hopes could help him broaden his appeal. Former New York Mayor Michael Bloomberg also endorsed Toomey this month through his Independence USA PAC, which focuses on gun laws. And in an ad from the group, Erica Smegielski, the daughter of the slain Sandy Hook principal, lauds Toomey for crossing party lines to support gun-control bills.

Giffords' PAC said Toomey would stand up to other members of his party.

"Our nation needs more Republican elected officials to stand with the vocal majority of Americans who support common-sense steps that help keep guns out of the wrong hands and prevent gun tragedies," said the PAC's executive director, Peter Ambler, in a statement from Toomey's campaign.




Staff writer Karen Langley contributed to this article.