The big question for Romney is New Hampshire. Does his campaign want to start driving up Giuliani and Huckabee's negatives now with risky paid mail and TV to try to pre-empt any bounce either could get from a strong second- or third-place finish in Iowa? (Assuming N.H. will follow Iowa by a few days.) Or does Team Romney wait and try to ride out the bumps? The scary scenario of a Huckabee upset and Giuliani third place in Iowa, followed by a Rudy or even Huckabee surge in New Hampshire, is looming. Rudy's squishy record as New York City mayor is indeed a big liability, but only if voters hear about it. The campaign clock is ticking. As the vulnerable Iowa frontrunner, Romney must both energize his own effort and slow down the competition's. That last part poses a very tough question: Does Mitt Romney want to get a political heart attack in January ... or give one?
Obviously, Romney doesn't want to play Dick Gephardt to Giuliani’s Howard Dean, launching a war of mutually assured destruction that allows McCain or Thompson to play the John Kerry role, grab an early upset, and sweep to the nomination. But if it hadn’t been for Gephardt (and that scream, of course), Howard Dean might have been the Democratic nominee in ’04, and the same goes for Giuliani this time around: If nobody goes negative on him before Iowa and Romney gets bloodied or even beaten by Huckabee, then the window for the Romney campaign to tear Rudy down will start closing fast. And since Romney’s probably the only candidate with the resources to give Hizzoner the negative-ad drubbing he deserves, if he stumbles early Rudy might just coast from then on out.
All of this assumes that things will be over in a hurry, of course, which as Marc points out isn't necessarily the case. The Ambinder "long campaign" scenario seems plausible at the moment; I would consider it not only plausible but likely if '04 hadn't happened the way it did. The day after John Kerry's tight win in Iowa, remember, it seemed like the race would drag on for a month at least, with Edwards and Dean and Kerry and maybe even Wesley Clark locked in an epic dogfight. But in reality it was already over: Momentum trumped everything else.
(On the other hand, the whole "we need to be united against Bush" dynamic seemed to play a substantial role in the Democratic electorate's rush to judgment three years ago, and for all the potency of Hillary-hating, it may not have the same "suck it up and vote for the front-runner" effect on GOP voters this time around.)