SIOUX CITY, Iowa (AP) -- Republican presidential front-runner Newt Gingrich clashed sharply with one rival, took pains to compliment another and said it was laughable for any of them to challenge his conservative credentials Thursday night in the last campaign debate before the Jan. 3 Iowa caucuses kick off the 2012 primary season.
In a forceful attack, Minnesota Rep. Michele Bachmann said Gingrich "had his hand out and received $1.6 million to influence senior Republicans and keep the scam going in Washington, D.C.," for Freddie Mac, a government-backed housing entity.
"Just not true," Gingrich shot back. "I never lobbied under any circumstances," he added, denying an allegation she had not made.
The clash underscored the state of race, with Gingrich, the former House speaker, atop the polls in Iowa and nationally, while Bachmann, former Massachusetts Gov. Mitt Romney and his other pursuers work in television ads and elsewhere to overtake him in the final days before the caucuses.
Former Sen. Rick Santorum of Pennsylvania, who has staked his campaign on Iowa, was quick to challenge Gingrich as a conservative leader. He recalled that Gingrich had to contend with a "conservative revolution' from the ranks of Republican lawmakers when he was House speaker in the 1990s.
Rather than going after Gingrich, Romney, who runs second in the polls in Iowa, said his experience in private business made him the man to confront President Barack Obama in debates in the fall of 2012. "And I'll have credibility on the economy when he doesn't," he said.
Given the stakes, Gingrich, Bachmann and Santorum weren't the only contenders eager to impress Iowa voters and a nationwide television audience with their conservative grit.
"I hope I am the Tim Tebow of the Iowa caucuses," said Texas Gov. Rick Perry, referring to the Denver Broncos quarterback whose passing ability draws ridicule but who has led his team to a remarkable seven wins in eight weeks.
"We're getting screwed as Americans," said former Utah Gov. Jon Huntsman, insisting that he, in fact, was a steadier conservative than any of the others on stage.
"Anybody up here could beat Obama," said Rep. Ron Paul of Texas, whose views verge on libertarianism and who has struggled to expand his appeal.
Indeed, the big question in the opening moments of a fast-paced two-hour debate went to the heart of a dilemma that could eventually settle the race -- do conservative Republican caucus and primary voters pick a candidate with their hearts, or do they look elsewhere if they judge their favored candidate might not be able to defeat the president.
Those voters begin making that choice on Jan. 3, and if experience is any guide, one or more of the presidential hopefuls on the debate stage will not make it out of the state to compete in the New Hampshire primary a week later.
Gingrich, who seemed an also-ran in the earliest stages of the race, has emerged as a leader heading into the final stretch of the pre-primary campaign. His decades in Washington and his post-congressional career as a consultant have been the subjects of tough critiques from Romney's campaign in the past week.
But the former speaker passed up an offer to criticize his rival on the issue of Medicare, saying, "I'm not in the business of blaming Gov. Romney." In fact, he said, Romney has made constructive suggestions for preserving the program that tens of millions of Americans rely on for health care yet faces deep financial woes.
Gingrich drew criticism earlier in the year for calling a GOP Medicare proposal "right-wing engineering." Romney refrained from criticizing that plan but did not embrace it in full.
Bachmann, who has long-since faded to the back of the pack in the polls, seemed most eager to confront Gingrich.
And when he labeled her charges inaccurate, she shot back that when she made similar contentions in the previous debate, she was judged factually accurate by an independent arbiter. She said Gingrich's work for Freddie Mac was in furtherance of a "grandiose scam" to keep alive an entity at the heart of the housing crisis.
"I will state unequivocally for every person watching tonight: I have never once changed my positions because of any payment," Gingrich said, adding that in fact, he favored breaking up both Fannie Mae and Freddie Mac, his benefactor.
Moments later, Bachmann challenged Paul even more aggressively, saying his views on Iran were a danger given the country's work on acquiring a nuclear weapon.
Iowa Gov. Terry Branstad, a Republican who has said he probably will not endorse a candidate before the caucuses, said earlier Thursday that Gingrich needs to show he has discipline in the next few weeks to convince GOP voters he has what it takes to be president.
"I don't know. I don't know," Branstad said in an Associated Press interview when asked specifically if he thought Gingrich had the discipline to be president. "I think he's a great idea person; I have a lot of respect for him. But whether he has the discipline and the focus, I don't know."
Romney has not begun running ads assailing Gingrich. But he has characterized the former speaker as "zany" for having endorsed mining the moon and lighting highways with mirrors in space.
Romney has increasingly looked to slow Gingrich in Iowa. Romney has campaigned lightly in the state, and some influential social conservatives there have doubts about his Mormon faith and changed positions on social issues.
In a new ad in Iowa, Romney is describing the need to reduce the federal deficit as a "moral responsibility."