One of the things that might not be immediately clear about Iowa is the extent to which it complicates Mitt Romney's general-election campaign, if he's the nominee. After all, it's clear that his strategy relies on a shift back to the center, where he'll run on his record as governor of Massachusetts.
For this to work, however, Romney needs to avoid the kind of right-wing rhetoric that defines candidates like Rick Perry and Newt Gingrich, which in turn, requires a quick and decisive path to the nomination, where he can avoid outsized commitments to right-wing priorities. If Romney had walked away from Iowa with a decisive win, this wouldn't be a concern. But the fact is that Iowa underscored the extent to which he is unpopular with the right-wing of the Republican Party, even if they're willing to support him (which they will, eventually).
In all likelihood, Romney will have to shore up the right flank of his campaign with a renewed emphasis on conservative rhetoric and a promise to pursue the priorities of right-wing Republicans. The problem for Romney is that having made a huge flip to the right wing during the primary, he'll have to make a comparable flop back to the center during the general election, and a flop of that magnitude is hard to explain to most voters. What's more, he'll continue to face pressure from distrustful conservatives, who doubt his commitment to their ideology. The more Romney is forced to accommodate conservatives, the more difficult it is to shift to the center.
Writing for The New Yorker, George Packer provides a concise view of this dilemma:
It would be a mistake, though, to believe that, long after Iowa, once the horse race is over, and if he's elected, Romney could suddenly flip a switch, clear the air of the toxicity left behind by the Republican field, and return to being a cautious centrist whose most reassuring quality is his lack of principles. His party wouldn't let him; and, after all, how a candidate runs shapes how a President governs.
The flip is always tolerable, but it's the flop that kills.