p>"When it came time to secure our borders, Steve Huffman was missing," says the Democratic ad, citing Huffman's absence during votes to fund border security technology and fix the immigration system. "If we can't trust Huffman to show up for work, how can we trust him to protect us?"

The ad is contributing to the particularly vitriolic tone of the race less than one week before the September 12 primary. Some analysts also say the ad might be evidence that Democrats believe Huffman will be harder to defeat than Randy Graf, a solidly conservative candidate who leads Huffman by more than 12 points, according to a recent Tucson Business/Wick Communications Poll. It's unclear whether Huffman will get a boost from the RNCC ads, which began running last week.

Other Republican candidates, meanwhile, have also continued their attacks on Huffman and the RNCC, which usually does not endorse a specific Republican candidate in a primary election. On Tuesday, Graf and three other candidates vying for the Republican nomination issued a joint letter skewering the RNCC's behavior. They called on RNCC Chairman Ken Mehlman to "immediately stop using Republican fundraising dollars to defeat fellow Republicans."

"Stay the hell out of southern Arizona," Mike Hellon, a former state GOP chairman, told reporters after a joint news conference focused on the letter. Hellon is also running in the Republican primary and consistently polls among the top three candidates.

Graf campaign manager R.T. Gregg also told U.S. News Wednesday that the Minutemen have now descended on the district and bought $50,000 of advertising supporting Graf. An immigration hawk, Graf has emphasized throughout the campaign that he was a founding member of the Minutemen.

Hellon, meanwhile, thinks the Republican sniping is only helping the Democratic candidates for the seat, a field currently led by former state Sen. Gabrielle Giffords.

"It's the granddaddy of unintended consequences," Hellon said Tuesday. Of the RNCC, he said, "They're idiots."