Rivals of surging Republican presidential hopeful Rick Santorum raised doubts about his conservative record in hopes of heading off a last-minute victory by the former senator a day before Iowa kicks off the 2012 presidential election season.
Read RTE's Washington Correspondent Richard Downes' campaign impressions here
Mr Santorum, a second-tier candidate until a jump in the polls last week, claimed the momentum as he and the other Republican candidates barnstormed across Iowa making final arguments and trying to bolster turnout ahead of Tuesday's Iowa caucuses.
Former Massachusetts Governor Mitt Romney and libertarian Congressman Ron Paul are neck-and-neck in the lead in Iowa polls.
But Mr Santorum, uniting voters on the Christian right who have been divided for months, is making a late move and could pull off a victory.
Texas Governor Rick Perry, who could suffer with a good Santorum showing, tried to slow the momentum of the former Pennsylvania senator, who lost his re-election bid in 2006.
Mr Perry told MSNBC that Mr Santorum's conservative credentials are in doubt because he backed costly government spending projects and supported the re-election of moderate Pennsylvania Republican Senator Arlen Specter, who voted for bank bailouts that conservatives disliked.
Mr Paul took aim at Santorum's conservative record, too, telling CNN: "He's very liberal ... He spends too much money."
Mr Santorum is peaking at the best possible moment, emerging from the pack as a conservative alternative to Romney after Perry, Newt Gingrich and Michele Bachmann have faltered.
At an event in Polk City, Santorum waved off Perry's criticism.
"Rick Perry is hammering away at me. That is what he has to do. That is what politics is about," he said.
After months of town hall events and debates and millions of dollars spent on TV ads, tomorrow's outcome was still difficult to predict. After all the attention on Iowa, only a small sliver of the electorate - perhaps 120,000 people or so - will participate.
Voters had a choice to make - go with their gut and vote for who they think is a strong conservative, or choose someone they think will be the most electable in the November general election against Democratic President Barack Obama.
Mr Paul, who has risen in popularity due to his anti-war positions, could benefit if Democrats and independents decide to enter the Republican race on his behalf.
He said in Des Moines that money was flowing into his campaign, which he called "a vote of confidence" and the enthusiasm was greater than during his 2008 presidential bid.
Mr Romney, who is more moderate and has establishment backing, looked to have a good day tomorrow under most scenarios.
He has spent far less time in Iowa than his rivals yet stands a chance to win the caucuses and go to his home turf of New Hampshire with a big head of steam.
Team Romney would love to pull off a surprising victory in Iowa but would consider a Paul or Santorum win good for Romney, since Romney aides consider Gingrich and Perry to be more dangerous rivals in the long run.
Mr Gingrich tried to puncture the image of Romney as the more electable Republican. Mr Gingrich tumbled out of the front-runner spot down to fourth place in the Des Moines Register poll after weeks of blistering attacks from Romney and others.
"People who describe him as the front-runner have to ask yourself the question, if you spent that many million dollars to get to 23%, how can he possibly think he's the most electable candidate?" he told reporters.
Mr Gingrich acknowledged he would not win and said he will stay in the race for the nomination no matter the result. He has been leading polls in South Carolina.
"What I do tomorrow night will be a victory because I'm still standing," he said.
Ms Bachmann, who won the August straw poll of Iowa voters, has fallen to last place in the state. She told the CBS "Early Show" she would stay in as well whatever happens in Iowa, saying she had already book airline tickets to South Carolina.
