The GOP has worried it may lose its Senate majority in November and Toomey may be one of the victims.

Sen. Pat Toomey (R-PA) has received an endorsement from former Democratic congresswoman Gabby Giffords as he faces a tough reelection in November.

The endorsement from Giffords and her anti-gun violence group Americans for Responsible Solutions might be just what Toomey needs to defeat his Democratic challenger Katie McGinty, who has slightly pulled ahead in four polls.

So why would the former Democrat Congresswoman choose the GOP incumbent over the Democrat?

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.”

A mentally ill man shot Giffords and 18 others in Tucson, AZ, in 2011. Six people died in the attack. Since then, Giffords and her husband have pushed for major gun restrictions across the country.

Their group said Toomey “broke from the gun lobby” in 2013 when he voted “to expand background checks to gun purchases online and at gun shows.” He responded:

“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.

McGinty and her campaign criticized the move, insisting “her positions on gun control are more in line with Giffords,'” and that Toomey is not 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.

FOX 29 reported:

Toomey opposed Democrats’ bills to close the terrorist loophole because, he said, of the barriers they would create for someone who is mistakenly put on a terrorist watch list and blocked from buying a gun.

Rather, Toomey supported a Republican measure to block such purchases, legislation that Democrats defeated and criticized as being ineffective. GOP leaders did not allow a vote on a proposed compromise bill Toomey drafted in June, and he sided with Democrats on another proposed compromise sponsored by Sen. Susan Collins, R-Maine. The NRA opposed Collins’ bill, and Republicans defeated it.

Toomey also has the backing of anti-gun billionaire Michael Bloomberg, the former mayor of New York City.

On Tuesday, Roll Call reported that they’ve changed the election from “Tilts Republican to Tossup.” McGinty has pulled ahead in four polls:

“Is Katie McGinty benefiting from Hillary Clinton’s 10 point lead over Donald Trump in Pennsylvania,” said Tim Malloy, assistant director of the Quinnipiac University Poll. “Is she engaging Sen. Pat Toomey in her own right, or is it a little bit of both? Any way you cut it, this first timer is giving the incumbent a run for his money.”