In what could be a signal that he's seriously competing in Iowa, Mitt Romney has aired his first negative ads against Rick Perry in the state, the Associated Press reports. And, naturally, it's hitting the Texas governor on the same issue that produced arguably their most memorable talking-over-each-other debate clash: illegal immigration. The AP's Tom Beaumont has the details on the ad, which will be a robo-call:

Arizona border-county Sheriff Paul Babeu speaks on the call, noting Perry's opposition to a fence along the U.S.-Mexico border and his support for in-state tuition for children of illegal immigrants.

Babeu says -- quote -- "Rick Perry is opposing a border fence and granting in-state tuition benefits to illegal immigrants. Rick Perry is part of the illegal immigration problem."

The move was immediately seen as a potential turning point for Romney's campaign in Iowa, which has played it cautiously in the state in 2012 after going all-in in 2008 and losing to Mike Huckabee. In New York magazine this past Sunday, John Heilemann outlined this dilemma, speaking to a Republican operative who deemed the state like "Lucy and the football" for Mitt Romney. He could go for broke, the theory goes, but like Charlie Brown end up falling flat if he tries too hard and fails.