Employing some of the toughest rhetoric to date, the Republican presidential candidates gave their closing arguments the day before the Iowa caucuses -- assailing President Obama as a "fraud" who is "dangerous" to the country while holding nothing back in their criticism of the rest of the GOP field.
The intensity of Monday's campaign trail sparring reflected the tension and uncertainty in the race.
No fewer than three candidates are in contention for the top spot and many Iowans are undecided, in one of the most volatile GOP campaigns in history. Those on the leaderboard also represent distinct wings of the Republican Party, making the contest as much a statement about the ideological direction of the GOP -- in Iowa, anyway -- as a ruling on which candidates should advance to the next round.
Despite Iowa's mixed record of picking winners, caucus-goers got the sense in the final hours that the candidates believe they have a lot riding on the results.
Rick Santorum, the former Pennsylvania senator who suddenly is surging in the polls, charged into the final stretch with the message that he represents something his opponents do not -- electability and conservative principles.
"I'm asking you to not settle for someone as your nominee who might be able to win the election, but the election would be a pyrrhic victory," Santorum said Monday in Polk City. "In other words, we wouldn't have a candidate who is going to be elected president who will do what's necessary of what America needs."
The comment was an apparent swipe at Mitt Romney, whom Santorum also challenged over his private-sector credentials. "We are not looking for a chief executive officer for this country. We're looking for a commander-in-chief," Santorum said.
Santorum went on to question whether candidates like Romney and Rick Perry could put together a coalition in a general election against Obama -- though similar questions have been raised about Santorum.
Going into the caucuses, the polls generally show Romney at the front of the GOP field, with Ron Paul and Santorum right behind him -- though a Public Policy Polling survey Monday showed Paul leading by 1 point.
While Santorum represents the social conservative wing of the party, Paul and Romney align more with the libertarian and fiscal conservative wings, respectively.
Paul, whose hands-off approach to foreign policy has come under attack as naïve, sprayed his opponents at a rally in Des Moines.
"Believe me, you don't have to worry about the choice if you choose another candidate, because the others represent the status quo," Paul said. "But they're not talking about a foreign policy to defend America. They're talking about mischief around the world and policing the world. ... They don't care about your personal liberty, or it wouldn't be continuously undermined." +
However, Paul later conceded that his path to the Republican nomination is uncertain.
When asked Monday during an ABC News interview whether he sees himself in the Oval Office, Paul replied: "Not really, but I think it's a possibility."
He added: "I don't deceive myself. You know what the odds are. The odds have been slim."
Romney refrained from targeting his primary opponents, keeping his message focused on the sitting president and his own economic vision for America. At one point, he described Obama's presidency as "just a detour, not our destiny."
Arguably the toughest criticism Monday came from the two middle-tier candidates fighting to break into a top-three finish in Iowa.
Perry, during a stop in Sioux City, accused Obama of sending the country on a path toward "bankruptcy."
"He truly believes if you print enough money that you will create jobs. And we will expose him for the fraud that he is every day," Perry said.
He balanced his criticism of Obama with shots at Paul and Santorum.
Perry predicted that if Paul wins the White House, "he will bring all of our troops back home, he'll bring the 5th Fleet back out of the Persian Gulf. And we will be living in the 1930's again."
On the stump and in a new online ad, Perry targeted Santorum's record of pursuing earmarks as a member of the U.S. Senate.
The online ad called Santorum "a porker's best friend" and ended with one word: "Unelectable."
Newt Gingrich, meanwhile, was in rare form. At one point, he conceded he does not think he's going to win Iowa, chalking up the rough odds to the glut of negative ads against him.
But the ex-House speaker touted his ability to compete nationally, saying any other candidate would be "an amateur in the Obama tradition."
He directly challenged Romney's on-again, off-again status as the race's frontrunner.
"Romney is proving decisively that the moderate vote is about 23 percent," Gingrich said. "He'll do somewhat better in the northeast and have one or two states where he does pretty well. But I think people who describe him as the frontrunner have to ask yourself the question -- if you spend that many million dollars to get to 23 percent, how could you possibly think he's the most electable candidate?"
Gingrich spent much of the day assailing the Obama administration, particularly over his aides' plan to base the president's early 2012 strategy on a contrast with Congress.
Gingrich accused the president of planning to govern without Congress, calling it "totally unconstitutional."
Santorum also took his shots at Obama, calling him the most "dangerous president since Jimmy Carter" when it comes to foreign policy.
Iowa Gov. Terry Branstad told Fox News that Santorum, who rose rapidly from only single digits in the polls, "did it the old-fashioned way" -- by traveling to every county in the state while other candidates were splitting their time.
"I think he will be one of the top three," Branstad said.
Michele Bachmann, who is trailing in Iowa despite winning the Ames Straw Poll over the summer, was out with a new TV ad in Iowa Monday in a last-ditch attempt to win back supporters. The ad stressed her Iowa roots and described her as a "consistent conservative fighter."
Out of the Iowa contest, the candidates head next into New Hampshire for the first-in-the-nation primary, and then South Carolina. Romney has dominated New Hampshire, though Santorum and others claim they will compete there. Former Utah Gov. Jon Huntsman, who is not campaigning in Iowa and is behind in the polls, has also staked his campaign on New Hampshire.
The Associated Press contributed to this report.