While he was the frontrunner in the 2012 GOP race, Mitt Romney could sit back and let his rivals beat each other up while he raised money. Now that Rick Perry is threatening to leave Romney in the dust, he may have to change his strategy.

The New Republic's Ed Kilgore says if Perry wins big in Iowa, which he's threatening to do, it could spell curtains for Romney.

Romney’s problems are more than just a matter of whether he waits until Nevada and New Hampshire to make his play for the nomination. Expecting a demolition derby of other candidates that will allow him to glide to victory is no longer particularly plausible, and it runs a high risk of creating an early one-on-one competition with Rick Perry in which Romney is in an exceedingly poor position. Aggressively contesting Iowa or, for that matter, going for broke in South Carolina and other conservative states, will require that Romney change his passive Hail-to-the-Chief campaign message to something far more comparative, and that doesn’t necessarily play to his strengths as a candidate.

What Romney could really use is a sustained and abrasive attack on his rivals by the mainstream media and/or by Democrats. But will Barack Obama do the candidate his team allegedly most fears the service of tearing down the alternatives? And will actual Republican caucus and primary voters whose right-wing champions are under fire flee them to the safe haven of the anodyne Romney? Probably not.

So at some point, and some time soon, Mitt Romney is going to have to begin making not only a more positive case for his candidacy but a comparative case by way of attacking his rivals. Bachmann and Perry are highly vulnerable to such attacks, but it’s not clear how well conservatives will react if it’s Romney making the case that the Minnesotan’s wacky religious views are beyond the pale, or that the Texan’s contempt for Social Security is a problem.