Huckabee is now expected to win. A few weeks ago a narrow loss here would have boosted his campaign, now it could end it. He does now figure (and even sometimes lead) in polling in other states, but a disappointing result in Iowa would be fatal. A narrow victory and he is still in the race. A big victory and he is starting to look like the favourite.
Romney's expectations are now lower than before. A narrow defeat would look like a good result, and could leave him on course to win New Hampshire. (If he loses both, it is difficult to see a realistic path back). A win would leave him looking credible for a sweep of the early states and, thus, clear frontrunner status.
I am not a believer in the idea that we should be on the look out for "this year's Howard Dean". But it is certainly possible that the hard hitting campaign the frontrunners and their proxies are waging could lead to some other candidate roaring into front place at the last minute. That would completely alter the shape of the race.
McCain has everything riding on New Hampshire, thus anything that looks like a good result in Iowa, even third place could do it, would help him. A collapse by one of the front runners that put him in the top two would make him favourite for New Hampshire and looking very credible indeed. Despite the importance of NH to his campaign, he remains a factor in South Carolina and Michigan, and has name recognition across the country.
Thompson has disappointed thus far, but is perhaps best placed to benefit from a collapse in Huckabee's vote. If that happens, he would be looking good for South Carolina and Florida, and maybe New Hampshire and Michigan.
Giuliani is the one candidate who can afford to sit out Iowa. Despite evidence that he is fading in national polls, he remains the only candidate with both name recognition (he shares this with McCain) and money and organisation (he shares this with Romney). These assets will make him competitive in the larger states which vote on Tsunami Tuesday. Ideally he wants the field as fractured as possible in the run up to that date. If one candidate sweeps all the earlies, that candidate will probably win the bulk of the Feb fifth states too. He wants to avoid his opponents - who are probably a majority - coalescing around one candidate. Romney remains his most dangerous opponent, because name recognition can be gathered overnight - money and organisation cannot.
Clinton wants to win, but more than anything she wants to her opponents to remain divided. If either Edwards or Obama drops out after Iowa the survivor has a real chance at beating Clinton Perversely this means third place is better for her than second. If she wins, especially if the other two remain evenly matched, she is probably unstoppable. If she comes a good third - especially if Edwards is first - she would probably still look very strong for New Hampshire. Even in winning she could lose, if the result was fatal to Edwards. Her nightmare is Obama beating her comfortably with Edwards trailing in a poor third.
Edwards and Obama both want to eliminate the other. Clinton's assets are formidable. There is a floor to her vote, which means she will probably win most states on Tsunami Tuesday if there are still two other candidates in the race. But there is a ceiling to her vote too. If all the anti-Clinton votes have rallied around one candidate she is certainly beatable.