Ken Buck, a Weld County prosecutor, is challenging former Lt. Gov. Jane Norton for the GOP Senate nod in Colorado. The RealClearPolitics poll average shows Buck up by seven points with just two weeks to go. But this race is far from over.

In recent days, Buck has stumbled: A joke he made about Norton’s “high heels” went viral and he was caught on tape calling those who question the legitimacy of President Obama’s birth certificate “dumbasses.”

On the “birther” front, Buck tells National Review Online that he regrets using the word “dumbasses,” but not the thought. “[Birthers] have come to my rallies about seven or eight times,” he sighs. “They have stood up and dominated the meetings. Instead of having a polite exchange, they come and are just all over that issue, making it hard for us to talk about the national debt and health care. . . . They are rude.” But if “birthers” are not “dumbasses,” then what are they? “They are wrong,” Buck says. “I don’t agree with them.”

As former Rep. Tom Tancredo, Buck’s longtime booster, jumps into Colorado’s gubernatorial race as a candidate for the American Constitution party, Buck, a tea-party favorite backed by Sen. Jim DeMint (R., S.C.), is also distancing himself from Tancredo’s third-party politics.

“If Tom stays in the whole way, and starts pulling a significant number of votes away, [his candidacy] might have an effect [on my race],” Buck says. “The worst effect would be if he turns Republican voters off and they decide to not vote at all.” Buck, who made his name as a tough enforcer of immigration laws, also says that he differs “slightly” with Tancredo on that issue: “While we both believe strongly in the need to secure our borders, Tom has a slightly different view on immigration. I’m in favor of developing a guest-worker program to get people into the country,” he says. “Beyond that, I don’t want to speak for what his views are.”

“I’m not a tea-party candidate,” Buck adds. “I have made it absolutely clear that I am a grassroots candidate – not picked by the Washington establishment, former elected officials, lobbyists, or D.C. powerbrokers.” Still, if Buck makes it to the upper chamber, he says he is open to joining a tea-party caucus. “I would have to see what its mission was, but I am certainly leaning that way at this point.”

The winner of the August 10 primary will face either Sen. Michael Bennet (D., Colo.), who was tapped to fill a Senate vacancy in 2009, or Andrew Romanoff, a former Democratic speaker of the state House. NRO profiled the race back in June.