At dawn on December 12, 2006, the holiday of Our Lady of Guadalupe, a heavily armed fleet of Immigration and Customs Enforcement (ICE) officers stormed the JBS Swift Greeley Beef Plant, the largest employer in the sleepy city of Greeley, Colorado. They arrived in riot gear, arresting 265 Hispanic workers and deporting dozens in a coordinated seven-city raid known as Operation Wagon Train, a key front in the Bush Administration’s “war against illegal immigration.” The largest ICE raid in US history ruptured the city, split apart families, drew national headlines, and sparked a heated debate inside the city, as Republican Mayor Tom Selders denounced the government’s heavy-handed tactics. One Hispanic activist told The Nation’s Marc Cooper, “This has been our Katrina.”

The raid was masterminded by Weld County District Attorney Ken Buck, Colorado’s new GOP nominee for the US Senate. Buck defeated former lieutenant governor Jane Norton in a hard-fought primary last night—and his hard-line stance on immigration was a big reason why. Yet his obsession with this issue complicates his bid to defeat the Democratic nominee, Senator Michael Bennet, and could potentially cost him the election in an increasingly diverse purple state.

Two years after Operation Wagon Train, Buck conducted a highly-publicized raid of Amalia’s Translation and Tax Services in Greeley—a tax office for Hispanic immigrants in the city—seizing thousands of confidential tax returns and arresting dozens of alleged illegal immigrants as part of Operation Numbers Game. The ACLU sued Buck and the Colorado Supreme Court later ruled that his search was unconstitutional. It was a major public setback for Buck, who spent $150,000 in county money unsuccessfully appealing an earlier district court decision. Nonetheless, his tough talk on immigration made him a darling of the Tea Party. “In Weld County, we know the difference between an illegal and a United States citizen,” Buck said to wild applause at the first Tax Day Tea Party in Denver on April 15, 2009. “I heard your voices in Weld County and I felt your prayers.” He’s since supported Arizona’s draconian new immigration law, which was recently blocked by a federal judge.

Now Buck will have to square his harsh anti-immigrant rhetoric and actions in a state where Hispanics make up 17 percent of the electorate and play an ascendant role in Colorado politics. He’s already managed to offend women in the primary; when asked—at the Independence Institute’s Alcohol, Tobacco and Firearms party, no less—why people should vote for him, he responded, “Because I do not wear high heels.”

It was a joke, just not a funny one. “She has questioned my manhood,” Buck said of GOP foe Norton. “I think it’s fair to respond. I have cowboy boots. They have real bullshit on them. That’s Weld County bullshit.”

You can say that again. At a time when Republicans are expected to pick up seats across the country this November, they just can’t seem to get their act together in Colorado.

—Ari Berman’s new book, Herding Donkeys: The Fight to Rebuild the Democratic Party and Reshape American Politics, will be published in October by Farrar, Straus and Giroux.