During last year's presidential election, Gomez acted as spokesman in a number of television interviews for the Special Operations OPSEC Education Fund, a group that criticized President Obama for his handling of the Osama bin Laden killing.

During a Tuesday campaign event, Gomez said he wasn't "part" of the group, the first time he's addressed his affiliation since Democrats began their offense.

“As far as OPSEC, I did two interviews for OPSEC. I was never associated with OPSEC. I never donated to OPSEC. I wasn’t part of OPSEC,” he said, according to the Boston Globe.

His opponent, Rep. Edward MarkeyEdward (Ed) John MarkeyA game theorist's advice to President Trump on filling the Supreme Court seat Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE, and national Democrats have sought to tag Gomez as anti-Obama because of his affiliation to the group, an argument that could complicate his appeal in Massachusetts, which Obama won with more than 60 percent of the vote in 2012.

Gomez said on Tuesday he gives Obama "full credit" for authorizing the mission to kill bin Laden, but continued to criticize the way he handled the aftermath.

“I was never connected with them in the first place. I just went on there because we overlapped on that issue about the president taking too much credit and, more importantly, they leaked information that was bad for the unit down there and it put their lives at risk,” he added.

Gomez's opponents have also worked to undermine Gomez's central rationale for his campaign, that he's a "new kind of Republican," by arguing that his affiliation with the group makes him "the poster boy for a radical superPAC airing special interest smear ads," as Democratic Senatorial Campaign Committee Spokesman Justin Barasky put it.

And Newtown Mayor Setti Warren (D), an Iraq War veteran, appeared at a campaign stop with Markey and charged that Gomez had defended "swift-boat" style attacks on the President.

"Gabriel Gomez may call himself a 'new kind of Republican,' but that requires more than just words, and the people of the Commonwealth aren't buying it," he said.

Gomez's campaign and national Republicans have attacked the Markey campaign for a web ad that, for a brief part of the video, shows Gomez's face next to a shot of bin Laden.