At the moment, according to Nate Silver's most recent forecast, Mitt Romney is in a dead heat with Ron Paul for first place in the Iowa caucuses. Both hold a 40-percent chance of winning the contest, though Paul holds a slight edge in most of the polls used by Silver. Even still, this is an abrupt change from most of the fall, when Romney was projected to lose the Iowa caucuses on account of his moderate background and opposition from evangelical Christians.
Iowa isn't a ticket to victory in the Republican presidential primary, but it does set the stage for the proceding contests. A world in which Romney loses Iowa is one in which his opponents (like Rick Perry) have a chance to block the former governor's path to the nomination with wins in states like South Carolina (which is similarly conservative) and Florida. But what if Romney wins Iowa? In that case, we can safely say that Mitt Romney is-or will be-the Republican nominee for president. A win in Iowa cuts off a challenge from the right, provides the momentum for an overwhelming victory in New Hampshire, and makes South Carolina a likely win as well. From there, it's like watching dominoes fall into each other; the momentum from one state carries into the next until Romney has accumulated the delegates necessary to win the nomination.
It's hard to say if this is good or bad for Romney's campaign. A long primary can strengthen campaigns, as they learn how to deal with attacks and crises, and extend their reach to voters around the country-this is essentially what happened with Barack Obama in 2008. That said, a long primary could also harm a campaign for the same reasons; attacks from all sides could leave voters with a negative view of the candidate. For Romney, it all comes down to whether his campaign is ready for a general election. Given the stakes, Democrats are sure to hit Romney hard from the beginning, in an attempt to define him to voters. If his team is ready for the struggles of a general election, this shouldn't be a problem. But if they aren't, then a quick win in the primary might have done more harm than good.