The newly recast field finds Romney, the former Massachusetts governor, reaching for a decisive victory in New Hampshire to solidify his status as the putative Republican front-runner. But his rivals threaten to block that quest.
One is former Utah Gov. Jon Huntsman, who skipped the Iowa caucuses and told voters Wednesday he could "smell success" in New Hampshire. Newt Gingrich, still reeling from a barrage of negative ads unleashed on him by a pro-Romney super PAC, bluntly dismissed Romney's efforts to cast himself as the most electable challenger to President Barack Obama.
"The fact is, Gov. Romney has a very limited appeal in a conservative party," the former House speaker said, setting aside his pledge to run a positive campaign to sharpen his criticism of Romney.
A pro-Gingrich super PAC sought to undercut McCain's endorsement of Romney, posting online an ad the 2008 Republican presidential nominee ran against Romney when the two competed for the party's nomination.
"Mitt Romney's flip-flops truly are masterpieces," said the ad revived by Winning Our Future.
Romney and McCain appeared together onstage Wednesday at rallies in Manchester and Peterborough. McCain won New Hampshire's primary in 2000 and 2008 and remains popular with Republicans and with independents, who can vote in the primary.
"The time has arrived for Republicans to choose a presidential nominee, a new standard-bearer who has the ability and determination to defeat President Obama," McCain said. The Arizona Republican was set to appear with Romney and South Carolina Gov. Nikki Haley at campaign events in that state Thursday.
The Iowa caucuses did little to clarify what has long been a fractured GOP field, with Romney and Santorum battling almost to a tie in that state and libertarian Texas Rep. Ron Paul placing third. The result demonstrated anew the difficulty Republicans have had in choosing between Romney, a former business executive who governed as a moderate, and a more dynamic, conservative alternative.
For now, Santorum has taken on that role.
The former Pennsylvania senator lost by just eight votes to Romney in Iowa, a strong showing due to a socially conservative message and dedicated politicking across the state's 99 counties. His challenge now is to raise money and build a strong enough organization to cement his status as a durable challenger to Romney.
At a Wednesday evening rally in Bretwood, Santorum urged supporters to keep the faith.
"Don't settle for someone who can win but then can't do, won't do and has no track record of doing the big things that are necessary to change this country," he said.
Santorum planned a full schedule of campaign stops across New Hampshire on Thursday. In TV interviews after his Iowa victory, he was challenged on his conservative views and record in Washington.
On CNN, he was asked about past comments equating homosexuality with bestiality.
"One can have desires to do things that we believe are wrong, but it's when you act out on things, that's the problem," Santorum said Wednesday.
He also defended so-called earmarks -- congressional spending designed to benefit lawmakers' home-state projects.
"When you go to Congress, you fight to make sure that when taxes go from your state to Washington, D.C., you fight to make sure you get your fair share back," he said, adding that he now opposes earmarks.
Santorum also suggested he had been misinterpreted while discussing Medicaid when he appeared to single out blacks for criticism.
Huntsman's schedule Thursday included staples of retail politicking in New Hampshire -- a Rotary Club breakfast in Hampton, a tour of a high-tech company in Durham, a business luncheon in Portsmouth and a town hall meeting in Newport.
After visiting businesses where audiences were more polite than enthusiastic, Huntsman ended Wednesday by rallying his campaign volunteers and showing off his campaign's first television ad.
Paul was headed to New Hampshire for campaign events after taking time off at home. Texas Gov. Rick Perry also went home after saying he would reassess his candidacy following a weak fifth-place finish in Iowa, but he later announced he would carry on. He planned to test his sputtering candidacy in South Carolina, which holds its primary Jan. 21, and was expected in New Hampshire for two debates this weekend.
"We're going to go into places where they have actual primaries and there are going to be real Republicans voting," Perry said, dismissing Iowa as a "quirky" place.
Iowa spelled the end for at least one candidate. Minnesota Rep. Michele Bachmann announced Wednesday she would step aside after placing sixth in Iowa, the state where she was born and where she won a Republican straw poll last summer.