Des Moines, Iowa ? Newt Gingrich tried to quiet unrelenting campaign criticism that he acknowledged had taken a toll as Mitt Romney stepped up insider attacks Saturday in hopes of regaining front-runner status with the first presidential vote little more than two weeks away.

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.”

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.”