Then an underdog named Huckabee, a one-time Southern Baptist preacher with right-flank credentials on social issues, struck a chord with voters who craved a rock-solid conservative. He recently soared past Romney in polls, and the race quickly took on religious overtones as Huckabee emphasized his Christianity and attracted influential evangelicals who view Romney's Mormon faith skeptically.

Romney shifted strategies and sought to ease concerns about his Mormonism by giving a high-profile speech on religion. He also started assailing Huckabee as weak on immigration and crime at campaign events and in the race's first negative TV ads. Romney's latest commercial takes Huckabee to task on foreign policy and government spending as well.

The effort may be paying off. Polls show Huckabee's double-digit lead is faltering.

Any erosion of support also could be attributed to Huckabee making several unforced errors, most notably on foreign policy matters. Or he simply may have peaked too soon.

By far, Romney has the strongest organization and the most money in a state where both are essential. But Huckabee has grass-roots networks of pastors, home-schoolers and gun owners working on his behalf. Each candidate is trying to lower expectations for himself while raising them for his rival.

Thompson has planted himself in Iowa in hopes the state can keep alive his lackluster bid. Neither Giuliani nor McCain has made the state a priority; they hope for better-than-expected showings. The trio is in a battle for the third slot, and any of them could seize it. They are mindful of the long-standing notion that there are only three tickets out of Iowa.

New Hampshire: Jan. 8

Next-up New Hampshire is a toss-up — between Romney and McCain.

The stakes are high for both. Romney, the former governor of a neighboring state who has a lakeside vacation home here, needs a win either to bounce back from an Iowa loss or, if he triumphs in the leadoff caucuses, to solidify his standing as the front-runner. He has had an edge for months after putting $6 million into ads and spending a year engaging in shoe-leather politics.

A loss for McCain would end his candidacy; he's pinned the fate of his second bid on the state he won in 2000, largely out of necessity after his campaign found itself broke and laying off staff over the summer. He has seen signs of a resurgence in recent weeks.

Both men will benefit from substantial get-out-the-vote operations, but McCain trails Romney dramatically in money.