Iowa fires the first shot of the 2012 battle for the White House on Tuesday with a keenly watched but unpredictable vote on which Republican should challenge President Barack Obama in November.
With half of this heartland state's voters still up for grabs, frontrunner Mitt Romney, 64, was locked in a neck-and-neck race with Representative Ron Paul and former senator Rick Santorum in the party's first nominating test.
The Iowa caucuses come against the backdrop of a sour, job-hungry US economy that weighs heavily on the embattled Obama's bid for a second term, four years after he promised his historic 2008 victory would offer "hope and change."
"He's out!" Romney, a former Massachusetts governor and millionaire venture capitalist, told cheering supporters at a rally in Des Moines, Iowa's capital, in the final countdown to Tuesday's caucus. "I will get America working again!"
Come 7:00 pm (0100 GMT Wednesday), Iowans from the state's 1,774 precincts will head to places like school gymnasiums and cafeterias or church basements to hear speeches from their neighbors on behalf of the seven candidates and then vote.
"A lot of people are going to walk in still trying to decide what's the right thing for America," former House speaker Newt Gingrich, who trails in the polls, told CNN. "So, I think we could win."
The quirky process's strength lies in its timing: As the first nominating vote, it can set the tone for the rest of the state-by-state battle, lift or bury a sagging campaign and add luster to a shining presidential prospect.
Santorum, a fierce social conservative who has surged in Iowa after once being given up as politically dead, predicted on ABC television he would "do very well" here and then carry that momentum into New Hampshire's January 10 primary and then "pour it on" in South Carolina on January 21.
Romney has made little secret that he hopes for a strong finish in Iowa, a romp in New Hampshire, and another success in South Carolina, which could help him get a lock on the nomination relatively early.
Paul's unorthodox libertarian views have earned him a devout following, but he is seen as uncompetitive in other states, while Santorum, 53, faces an uphill fight to match Romney's massive national organization.
Still, while Romney's massive campaign warchest and high-profile endorsements have fed his image as the candidate to beat, he faces stubborn doubts about his conservative credentials, as well as his Mormon faith, and has been unable to increase his support among Republican voters nationwide above 30 percent.
Obama "will just tear him apart. I mean, he will not survive against the Obama machine," Gingrich, angry about a relentless barrage of attacks ads run by Romney's allies, told CBS.
Paul, 76, a small-government champion opposed to foreign aid and military interventions overseas, has accused the other candidates of supporting a foreign policy of "mischief around the world and policing around the world."
"Most of the rest of the Republican field seems to be a little bit over eager to use nuclear weapons and to bomb other countries," Republican Senator Rand Paul, the candidate's son, told CBS television.
The candidates made a final blitz across Iowa, mindful that the winning margin in the 2008 caucus was 10,000 votes out of just 120,000 cast -- a fraction of Iowa's two million registered voters.
"It's very fluid," Representative Michele Bachmann, a long-shot candidate, told CNN. "There's a long way to go. I have a lot of staying power."
"We are going to take America back. That's what this is about. It is a powerful moment in America's history. And you are on the front lines," Texas Governor Rick Perry, who also lags in the polls, told volunteers.
Iowa -- where unemployment is well below the national average -- is also an unreliable predictor of presidential fortunes: Senator John McCain, the eventual nominee in 2008, came in fourth that year.
The state's Republican Governor, Terry Branstad, noting that winning the state catapulted Obama's historic 2008 presidential bid, told CNN: "Iowa launched Obama. I think Iowans want to sink Obama. They're not happy."
Obama, who is unopposed in the Democratic caucuses in Iowa, was planning to address his supporters later in the day by video conference at 0115 GMT as he seeks to inject momentum into his bid for re-election.
Former US envoy to China Jon Huntsman skipped Iowa in favor of focusing on New Hampshire, where Romney enjoys a considerable lead.