PEWAUKEE, Wis. (AP) — Republican U.S. Senate candidates Leah Vukmir and Kevin Nicholson clashed during closing statements at the end of an otherwise staid first debate Thursday, with former Democrat Nicholson defending his conservative credentials while Vukmir said her record in the Legislature proves she can be trusted.

Both hopefuls went about 10 minutes over time at end of the hour-long debate in a spirited back-and-forth after Vukmir said, "We can't take chances on the unknown."

That prompted Nicholson, a former Marine, to respond: "I feel like I might be the unknown in that variable. I am. I'm clearly different, folks. Clearly different kind of candidate. That is what we need. ... You all knew this when you voted for Donald Trump."

While they largely agreed on most of the issues, Nicholson stressed that he would be an outsider who would buck GOP leadership to stand up for his conservative principles. Vukmir, a 15-year veteran of the Legislature and close ally of Gov. Scott Walker, emphasized her record introducing and voting for a bevy of conservative priorities. She said "I've seen it, I've done it and I'm going to do it in Washington."

And she pushed back after Nicholson criticized the party establishment and cited the loss earlier this month by the Republican-backed candidate for Wisconsin Supreme Court.

"You know what my track record is," Vukmir said. "We know more about Kevin's track record as a Democrat than we do about his track record as a Republican. I think that is the issue, who can you trust to follow through."

Nicholson retorted that his track record was on the battlefields of Iraq and Afghanistan.

"I know that doesn't mean much to certain politicians," he said, eliciting a smattering of boos from the audience of more than 300.

"That's wrong," Vukmir said. She later called for Nicholson to apologize for inferring she didn't respect his service in the Marines.

"If it makes you feel better," Nicholson said, "I feel respected." And with that, the debate ended amid more boos from the crowd.

The winner of the Republican primary on Aug. 14 will advance to take on Democratic Sen. Tammy Baldwin.

Vukmir has focused her campaign on winning the backing of longtime, grassroots Republicans, and she reminded them of the issues they care about that she fought for as a member of the Legislature.

"I stood shoulder to shoulder with Governor Walker when we broke the stranglehold of public sector unions," Vukmir said, referencing the 2011 law known as Act 10 that effectively ended collective bargaining for most public workers.

Both Nicholson, 40, and Vukmir, whose 60th birthday was Thursday, praised Trump's imposing of tariffs on China and his promise to build a wall along the Mexican border.

The debate, livestreamed by its sponsor the conservative group Americans for Prosperity, comes two weeks before hundreds of Republican activists were to gather for the state party convention to vote on whether to endorse Nicholson or Vukmir.

Vukmir has been aggressively courting delegates to win the endorsement, which would give her candidacy a boost and provide her with contacts, staff and other resources of the state Republican Party.

Nicholson has all but conceded the endorsement to Vukmir and instead argued that anything less than 85 percent support would be a disappointment.