On the Republican side, Romney had blanketed the state with television advertisements and, with a nod to the way campaigns are normally won here, built an extensive get-out-the-vote operation that carted Romney's supporters to the polls all days. As polls showed Huckabee rising, Romney responded with a month-long barrage of ads attacking him on immigration and taxes.

"Congratulations on the first round to Mike," Romney said on Fox News.

Huckabee's populist appeal — powered by support from evangelicals — out-muscled a political operation that Romney spent more than a year building. Polls of Republicans entering the caucus sites found that nearly 60 percent described themselves as evangelical, and by overwhelming numbers they said they intended to vote for Huckabee.

A survey of Democrats entering the caucus sites found that more than half said they were attending their first caucus — and they divided with about 40 percent for Obama and about 30 percent for Clinton.

There was also a sharp generational break in support of the two candidates. Obama was backed by 60 percent of voters under 25 while Clinton was supported by about 45 percent of voters over 65.

Among Democrats, nearly half of respondents said that their top factor in choosing a candidate was someone who could bring about change; Obama won the support of about half that group. Just 20 percent said the right experience, Clinton's key argument, was the main factor; among that group, nearly half chose Clinton.

For all the talk about electability, barely one in 10 respondents said it was the main factor in their decision. Clinton and Edwards had an edge over Obama in this area.

Among Republicans, 6 in 10 described themselves as evangelical Christians; they went overwhelmingly for Huckabee. Huckabee was also supported by more than half of the Republican caucus-goers who said it mattered a great deal that a candidate shared their religious beliefs.

The personal quality Republican voters said mattered most in a candidate was that they shared their values. What mattered second most was that a candidate said what he believed. Huckabee outpolled Romney in both of those groups.

The Republican race was relatively straightforward. Romney and Huckabee were the main contestants, with none of the other candidates devoting much time or money to the state. Former New York Mayor Rudolph Giuliani made intermittent efforts here. McCain at one point all but wrote off the state, but returned after he won the endorsement of The Des Moines Register and saw, with the rise in polls of Huckabee, an opportunity to finish third.