It's crunch time for Republican presidential candidates, trying to win over undecided voters in Iowa.

It's the last full day of campaigning before the state's critical caucuses Tuesday.

Mitt Romney, often accused of having a "robotic" personality, has been trying to take on a warmer persona as he clings to his lead. He got some laughs in Iowa at the expense of President Obama, calling the gap between Obama's promises and his performance the "largest I've seen since the Kardashian wedding and the promise of 'til death do us part.'"

The latest Des Moines Register poll shows Romney ahead of the pack with 24 percent of the vote--but with Ron Paul right on his tail at 22 percent. With 15 percent, Rick Santorum is in third, but hopes a last minute surge will propel him to victory.

Newt Gingrich, who once held a commanding lead in Iowa before falling hard--not unlike the frontrunners who came before him--has declared that he "can't imagine being threatened by Rick Santorum." Gingrich says he'll be staying in the race no matter where he finishes Tuesday.

Michele Bachmann and Rick Perry are hoping for a miracle after sinking to the bottom of the polls. Both worked Sunday to court evangelical voters, a group which made up more than half of Iowa's caucus goers four years ago.