Along the way, Edwards showed signs that he was more concerned with competition from Obama than from Clinton. Asked directly by a voter whether he could beat Obama, Edwards said, "Oh, yeah, I can beat him." Both men are engaged in a spirited fight to win over second-choice voters.

If the Democratic race remained unpredictable, the outlook for the Republican contest was also murky. With a captive audience in Iowa, Huckabee's last-minute trip to California added to the mystery behind his campaign strategy, but he said his appearance with Jay Leno would reach more voters than a day on the campaign trail.

Before he boarded his plane in Iowa, however, Huckabee announced his support for the striking television writers union and said he identified with the striking workers because he is an author. He said he was unaware that he would be crossing picket lines because of the strike.

Huckabee's inconsistency or ignorance about the picket lines outside the Leno show are the latest in a string of missteps that have underscored the ad-hoc, on-the-fly nature of his insurgent campaign.

Speaking to reporters in Bettendorf, Romney ridiculed his rival's out-of-state trip on the eve of the caucuses. "Frankly, my focus is on the caucusers here in Iowa," he said. "I think Mike is more concerned about the caucus in Los Angeles."

While the Iowa caucuses take place five days before the New Hampshire primary, Romney opened his news conference attacking his main rival in New Hampshire, McCain, rather than Huckabee, who is his leading foe in Iowa.

"Welcome to Iowa, Senator," said Romney, who criticized him for sponsoring the immigration reform bill in the Senate that would have offered a pathway to citizenship for illegal immigrants provided they cleared certain hurdles. His stance on immigration was among the reasons McCain limited his campaigning in Iowa, focusing instead on New Hampshire.

For all the back-and-forth among those candidates, though, perhaps the biggest uncertainty in the Republican field rests in the candidacy of Rep. Ron Paul of Texas, who has raised $19 million. On city billboards and on signs planted along roadsides and in fields across Iowa, Paul's visibility has soared in recent weeks, raising worries among his Republican rivals about the strength of his movement.