Gingrich, the former House speaker enjoying a late surge in the polls, pledged to correct what he said were his rivals' inaccurate claims about him. Romney, the ex-Massachusetts governor looking for a rebound, portrayed Gingrich as a well-heeled lobbyist since his service in Congress and predicted that conservative voters will reject Gingrich as they learn more about his lengthy Washington record.
"I'm going to let the lawyers decide what is and what is not lobbying, but when it walks like a duck and quacks like a duck, typically it's a duck," Romney said.
With the Iowa caucuses Jan. 3 up for grabs, most candidates are redoubling their efforts heading into the holidays, when voters generally tune out the race.
Gingrich is their prime target. Last week alone, anti-Gingrich ads from a Romney ally outspent Gingrich by an 8-to-1 margin on television.
Gingrich cited "the extraordinary negativity of the campaign" during a call from Washington with Iowa supporters. He said he was inclined to hold teleconferences every few days so people can discuss ideas and his campaign can "encourage them to raise any of these things that you get in the mail that are junk and dishonest."
"I'll be glad to personally answer, so you're hearing it from my very own lips," he said in the forum. "We don't have our advertising versus their advertising, but you get to ask me directly."
Romney campaigned in early-voting South Carolina, where tea party activists have given Gingrich a strong lead in polls. Romney told reporters that many voters now are just beginning to pay attention to the race and will turn on Gingrich after they learn about his time in Washington and his role with mortgage company Freddie Mac, a quasi-government agency.
Gingrich's consulting firm collected $1.6 million from the company. Gingrich insists he did not lobby for them and only provided advice.
"I think as tea partyers concentrate on that, for instance, they'll say, `Wow, this really isn't the guy that would represent our views,"' Romney said after a town hall meeting with South Carolina Rep. Tim Scott. "Many tea party folks, I believe, are going to find me to be the ideal candidate."
Gingrich said the attacks on his record have been brutal, but he insisted they are exaggerated.
"I just want to set the record straight," Gingrich told his Iowa backers. "We were paid annually for six years, so the numbers you see are six years of work. Most of that money went to pay overhead - for staff, for other things. It didn't go directly to me. It went to the company that provided consulting advice."
It's a distinction without a difference, his rivals have said. Minnesota Rep. Michele Bachmann continued to criticize his tenure as a consultant and Texas Rep. Ron Paul continued an ad accusing him of "serial hypocrisy" for taking Freddie Mac's checks.
During a Friday appearance on Jay Leno's late-night television show, Paul also turned on Bachmann.
"She doesn't like Muslim. She hates them," said Paul, who routinely clashes with his rivals over foreign policy. "She wants to go get them."
Bachmann told reporters in Estherville that was not true.
"I don't hate Muslims. I love the American people," she said. "As president of the United States, my goal will be to keep America safe, free and sovereign."
Texas Gov. Rick Perry rumbled through rural Iowa on a bus tour. Former Pennsylvania Sen. Rick Santorum stuck to a plan that has won him the honor of spending the most time in the state, yet has not yet translated into support in polls.
Iowa's largest newspaper, The Des Moines Register, announced its endorsement of Romney on its website Saturday evening. It was as much an endorsement of Romney as it was an indictment of his competitors.
"While other candidates have pandered to extremes with attacks on the courts and sermons on Christian values, Romney has pointedly refrained from reckless rhetoric and moralizing," the newspaper wrote.
The paper does not have a track record of predicting winners in Iowa. In 2008, the paper backed Republican Sen. John McCain and Democratic Sen. Hillary Rodham Clinton. Four years earlier, it backed Sen. John Edwards' unsuccessful bid and in 2000 editors backed McCain and Democratic Sen. Bill Bradley. All came up short.
Former Utah Gov. Jon Huntsman, who early on decided against competing in Iowa, was campaigning in New Hampshire. Huntsman, who also served as President Barack Obama's ambassador to China, has kept his focus on New Hampshire, where independent voters are the largest bloc and can vote in either party's primary.
As the Iowa vote neared, Gingrich's decision to take the weekend off from campaigning raised eyebrows given his rivals' busy schedules. Gingrich called the decision "pacing."
Gingrich has prided himself on a nontraditional campaign, but his advantages in the polls could shift if the only exposure to Gingrich comes through rivals' negative ads.
Gingrich's campaign manager noted the onslaught in a fundraising pitch to donors.
"With Newt's opponents spending $9 million on attack ads in Iowa, we need to quickly ramp up our messaging," Michael Krull said Saturday.
Anti-Gingrich ads, courtesy of Romney allies, dominate in Iowa. The Restore Our Future political action committee on Friday spent an additional $1 million on airtime, and broadcast almost $790,000 in commercials against Gingrich last week alone. Gingrich, by comparison, spent roughly 100,000 on broadcast and cable ads.
That looked to continue into the final week before the Christmas holiday.
Romney, who has kept Iowa at arm's length after investing heavily here four years ago only to come up short. His advisers note they have kept in touch with supporters of his 2008 campaign that came in second place in Iowa.
Hunt reported from Charleston, S.C.