Des Moines, Iowa (CNN) -- Mitt Romney on Monday rallied supporters in Iowa on the eve of that state's caucuses, encouraging them to get out the vote and speaking confidently about his chances to earn the GOP's nomination for the presidency.
"I need a great showing here," Romney told a crowd of 400 voters in the Cedar Rapids-area community of Marion. "We're going to win this thing with all of our passion and strength, and do everything we can to get this campaign on the right track to go across the nation and to pick up other states and to get the ballots I need and the votes I need to become our nominee."
Romney approaches Tuesday's Iowa caucuses -- which kick off the GOP's 2012 presidential caucus and primary season -- as the apparent front-runner in recent polls, with U.S. Rep. Ron Paul of Texas running a close second and a surging Rick Santorum in third.
Candidates have campaigned across Iowa in the final hours before Tuesday's contests, with the top three trading barbs and former front-runner Newt Gingrich -- whose support dipped in polls in recent days amid numerous attack ads -- conceding he won't win Iowa but asserting he is a survivor and will be in good shape for the long run.
A Des Moines Register poll released Saturday showed Romney, a former Massachusetts governor, at 24% support, with Paul close behind at 22%. Santorum, the latest to rise in a campaign that has seen several candidates enjoy bursts of support in political polls, had 15%, with Gingrich, a former U.S. House speaker, at 12%, and Texas Gov. Rick Perry at 11% and Rep. Michele Bachmann of Minnesota at 7%, according to the paper's survey.
Santorum, a former U.S. senator from Pennsylvania, was on the attack early Monday as he tried to claw his way into the top tier of candidates. At a campaign event Monday in Polk City, Santorum went after Romney without naming him.
"I know one of my opponents who has now directed his attention to me, surprisingly, has said that he has executive experience," Santorum said of Romney. "We are not looking for a chief executive officer for this country. We are looking for a commander in chief.
"We are looking for someone who has experience, someone who can lead. Someone who can lead our military but also someone who can lead in convincing the American public and the Congress to do the things that are necessary to transform this country, and that's not what CEOs do."
Later Monday, Santorum, a father of seven surviving children, received an apology from a Fox News contributor who had criticized him for events following the 1996 death of Santorum's prematurely born son.
Alan Colmes said Monday on Fox News that Republicans would shun Santorum when they learned of the "crazy things he's said and done," and claimed Santorum took the baby's body home, after the baby lived for only two hours, and "played with it for a couple of hours so his other children would know that the child was real."
Campaigning in Newton, Iowa, Santorum and his wife choked up Monday when an attendee asked him about Colmes' criticism. He described Colmes as insensitive and gave a much different picture of the loss, which his wife had previously described in a book called "Letters to Gabriel."
"We kept little Gabriel with us (at a hospital) that night, and we brought him home the next day," Santorum said. "We brought him home so our children could see him."
Santorum went on to tell the story about burying the child the following day.
"To some who don't recognize the dignity of all human life, who see it as a blob of tissue that should be discarded and disposed of, this is somehow weird. Recognizing the humanity of your son is somehow weird, somehow odd, and should be subject to ridicule," Santorum said.
Asked about Colmes' remarks after the event, Karen Santorum said, "I hope and pray he would never lose a child, that only parents who've lost a child understand the heartbreak, and they will understand that you go through an extremely difficult period, almost a temporary insanity, you try to make the best decisions you can to grieve that loss. It's huge, and it's profound.
Colmes posted on Twitter later Monday that he had apologized to the Santorums.
Santorum's campaign said it is raising more money as he surges in the polls. A senior Santorum adviser said the campaign raised more money in the last week than it raised online the past six months, adding that fundraising is between 300% and 400% higher on a daily basis than it was 10 days ago.
The infusion in funds has allowed the Santorum campaign to launch closing campaign commercials in Iowa. TV spots also are up in New Hampshire, which holds its primary on January 10, and the campaign is making ad buys in South Carolina, which holds the third contest, on January 21.
With Santorum at his heels, Paul called the conservative former senator a "liberal" in an interview Monday with CNN's Dana Bash. Paul was at a whistle-stop tour with his son, U.S. Sen. Rand Paul, R-Kentucky.
"(Santorum) spends too much money," Ron Paul said when asked what makes Santorum liberal. "He wasn't leading the charge to slash the budgets and vote against big government."
Later Monday, at a rally in Cedar Falls, Iowa, Paul's son seemed to refer to Santorum when he talked of "candidates trotting around, including one who seems to be rising in the polls in Iowa, who voted to double the size of the Department of Education, who's voted for foreign aid."
"Anybody in here think we need to be sending aid to other countries right now?" asked Rand Paul, campaigning for this father, known for noninterventionist views and a plan to eliminate the Education, Interior and Energy departments, among others. "We can barely take care of our own problems."
Romney, at a Dubuque rally Monday, focused his attacks on President Barack Obama.
"This president inherited a tough economy, but he didn't make it better. He made it worse," Romney said. "We're going to bring it back again by reapplying the principles that made us the great nation we have always been, by relying on free people, and free enterprises, (and) by remaining an opportunity society."
But Romney, who for the most part has left attacks on Republican rivals to surrogates and political action committees that support him, took shots at the other candidates in the GOP field at an event Sunday in Atlantic. He contrasted his record with that of Santorum's.
"Like Speaker Gingrich, Sen. Santorum has spent his career in government, in Washington," Romney told reporters. "Nothing wrong with that, but it is a very different background than I have."
Meanwhile, Perry is to trying to keep Santorum from pulling away from a near-three-way tie with him and Gingrich by questioning Santorum's voting record on earmarks in the Senate.
During an interview Monday on MSNBC, Perry also pointed to Santorum's double-digit loss when he tried to recapture his Senate seat in 2006.
"His ... argument is, 'I'm the guy that can win,' " Perry said of Santorum. "He got beat by 18 points in his last race. I mean, this guy has proven that he can't win races when it matters against a liberal Democrat."
Gingrich, whose strong debate performances saw him rise in polls before dropping amid a withering onslaught of negative ads and rivals' attacks, told reporters Monday in Independence, Iowa, that he wouldn't finish first on Tuesday. But he said that "whatever I do tomorrow night will be a victory because I'm still standing."
Gingrich also appears to be taking off the gloves after initially adopting a strategy of staying positive.
"Despite $3.5 million in negative ads by Romney, we are in fact beginning to bounce back, and we will clearly do well enough," Gingrich said in Iowa on Monday. "I don't think anyone else in this campaign could have taken the sheer volume of negative ads and still be in the race, and so I am very proud of the people in Iowa for seeing through the attacks and the negativity."
The former U.S. House speaker, whose rise also had been fueled by a conservative wing of the party that still has reservations about Romney, said the ex-Massachusetts governor "is proving decisively that the moderate vote is about 23%."
"He will do somewhat better in the Northeast and have one or two states where he does pretty well," Gingrich said. "But I think people who describe him as the front-runner have to ask yourself the question: If you spend that many million dollars to get to 23%, how could you possibly think that is the most electable candidate?"
Paul, meanwhile, has been calling his rivals' attempts to discredit his foreign policy and other views as desperation and demagoguery.
With Paul's rise to the top tier, rivals have attacked his noninterventionist views on foreign policy and less aggressive stance on Iran's nuclear program. They've also pointed to newsletters published under Paul's name in the 1990s that included racist comments. Paul has said he was unaware of the content of the newsletters at the time and rejected the content.
In an interview Sunday with Candy Crowley on CNN's "State of the Union," Paul drew contrasts between what he called his consistent positions and those of his rivals, and said opponents are desperate to find ways to attack him.
"They've been all over the place. They've been flip-flopping and they can't defend themselves," he said. "They're having a little trouble finding any flip-flops on me, so they have to go and dig up and distort and demagogue issues."
Bachmann, running at the back of the pack, is predicting a "miracle" finish in the state that launched her campaign over the summer.
Bachmann, one of the most frequent of Iowa visitors in the race to the White House, is a strong social conservative and often touts her history as a foster parent as well as her Iowa roots during campaign stops.
On Monday, Bachmann's campaign launched in Iowa a new TV commercial titled "Iron Lady," a reference to the famously strong former British Prime Minister Margaret Thatcher. The ad touts her Hawkeye State roots and conservative credentials.
Ex-Utah Gov. Jon Huntsman, a former U.S. ambassador to China, isn't competing in Iowa but instead focusing efforts on New Hampshire, which votes a week after Iowa.
Huntsman's poll numbers have edged upward in New Hampshire in recent weeks, but he has failed to break into the top tier. Romney has consistently held a large lead in polls there.
On Monday, two GOP sources told CNN that Romney would campaign in South Carolina this week after the Iowa caucuses, a sign that he is confident in winning New Hampshire next week.
Whoever wins Iowa's nomination will do so without the coveted endorsement of U.S. Rep. Steve King, R-Iowa.
The popular conservative announced on Twitter Monday that he won't endorse anyone ahead of Tuesday's contest.
Earlier Monday, he characterized the race as a game of "king of the hill."
"If you're at the top of the hill, everybody has to try to pull you down, and your negatives get illuminated and a lot of scrutiny goes on," King told Soledad O'Brien on CNN's "Starting Point."
"If you have five or six people trying to pull you off the hill, eventually they do that; someone else takes the top of the hill."
King said front-runner Romney has hung around the top of the hill.
"He hasn't actually claimed the top of the hill and (decided) he was about to own it until about now."
CNN's John Helton, Gabriella Schwarz, Dana Bash, Peter Hamby, Ashley Killough, Josh Levs, Shawna Shepherd, Paul Steinhauser, Rachel Streitfeld, Chris Welch and Jason Hanna contributed to this report.