Despite Romney's deep war chest, his well-oiled political machine, his sheen of electability and a disciplined, almost completely gaffe-free campaign — significant numbers of the party's primary voters still don't like him.
While Romney was neck-and-neck for much of the night with Santorum and Ron Paul, 75 per cent of those who cast ballots in the Iowa caucuses voted for someone other than the frontrunner.
Romney ended up eking out the narrowest of victories against Santorum, a former Pennsylvania senator who was the latest candidate to benefit from the "anyone but Romney" movement that's been a hallmark of the Republican race since it kicked off last spring.
Each man took 25 per cent of the vote, with Romney winning by a mere eight votes, while Paul, the libertarian congressman from Texas, took 21.5 per cent. There are no recounts in the Iowa caucuses; it took officials until 2:30 a.m. ET to announce the winner in the closest contest in the state's history.
Victory in Iowa is something Romney failed to achieve in 2008, a loss that wounded his campaign since the caucuses often give a candidate a boost of momentum heading into the New Hampshire primary a week later.
Iowa's many evangelical voters suspect Romney is a dreaded moderate; that isn't the case in New Hampshire, whose voters aren't nearly as socially conservative. The issue, however, could rear its head again in the South Carolina primary on Jan. 21.
The New Hampshire primary, indeed, is considered Romney's to lose given his rivals face a political organization that has grown ever mightier since 2008, when he lost that contest to John McCain. Romney has had a huge lead in New Hampshire polls for months, and Santorum isn't expected to catch up in a week.
But Romney is now in the crosshairs of a man who blames him for his failure to remain a contender — Newt Gingrich. The former speaker of the House of Representatives has been spitting mad at Romney for days, accusing him and his "millionaire friends" of being behind a series of negative ads he believes deflated his own unexpected surge among primary voters.
Gingrich has all but declared war on Romney, assailing his foe's continuing failure to win over a large number of primary voters in an email late Tuesday to supporters. Gingrich finished fourth on Tuesday night and reportedly left the state of Iowa in a huff after branding Romney a liar earlier in the day.
On Tuesday night, he didn't let the matter go, making reference to the "avalanche of negative ads" as he addressed his supporters while praising Santorum for waging a "great, positive campaign."
"I wish I could say that for all the candidates," he said before resurrecting the accusations against Romney in what seemed a particularly ungracious concession speech that also took aim at Paul's foreign policy stances.
Romney, for his part, brushed off Gingrich's fits of pique.
"I know the speaker's angry," he said earlier Tuesday. "I don't know why. But my anger's going to be focused on President Obama's failures to put the American people back to work."
Paul's third-place finish, meantime, didn't appear to have discouraged him or his young, loyal supporters. The upbeat Paul praised them for the "energy you have and the effort you have made" as they cheered when he urged the U.S. to get out of overseas conflicts.
"This movement is going to continue and we are going to keep scoring, just as we have tonight," Paul, 76, told them at the end of the night.
The night was a particular, and unexpected triumph for Santorum; however, it's one he owes mostly to timing.
Michele Bachmann, Rick Perry, Herman Cain and Gingrich before him have all briefly pulled past Romney, but Santorum's moment in the sun was fortuitous, taking place in the days before the Iowa caucuses.
Paul has been polling high in Iowa for months, while the socially conservative Santorum, who campaigned hard in the state, ascended from the basement of the public opinion surveys to win.
He thanked God and his wife on Tuesday night for his strong showing in Iowa.
The state's Republican primary voters got the first kick at the can in selecting the party's presidential nominee as they began casting votes in districts across the state at 8 p.m. ET.
The Iowa caucuses have far from a perfect track record in predicting a party's ultimate victor but the vote is nonetheless considered an important barometer of the hearts and minds of primary voters following months of wooing from the candidates.
Mike Huckabee won the 2008 Iowa caucuses, but McCain triumphed in the New Hampshire primary a week later and went on to win the party's nomination. Obama, meantime, won in Iowa in 2008, while Hillary Clinton took the New Hampshire primary.
Some argue the Iowa caucuses' primary function has been to either douse or spark candidacies rather than to forecast the party's ultimate nominee. Perry, for example, finished fifth in the caucuses on Tuesday and said he planned to "reassess" his campaign, suggesting he might now drop out of the race.
Many have assailed the Iowa caucuses, saying they give too much power to a minuscule number of fringe voters in a state that is otherwise politically insignificant.
The winning candidate doesn't even get awarded official delegates in Iowa because the caucus votes aren't binding. What the candidate does gain, however, is precious momentum heading into the New Hampshire primary, where delegates await.
Bachmann, the Iowa-born congresswoman, finished second last in the Iowa caucuses; only Jon Huntsman did worse, and he didn't campaign in the state in order to focus on New Hampshire.
Huntsman suggested Tuesday night that New Hampshire might represent his moment in the sun, likening his campaign efforts in the Granite State to Santorum's in Iowa.
"We've done the same type of work here," the former Utah governor told reporters.
He added he doesn't expect to win the state, but said a strong showing would allow his campaign to "come out of New Hampshire with a head of steam."