SIOUX CITY, Iowa (AP) -- Likening himself to Ronald Reagan, Republican front-runner Newt Gingrich insisted in campaign debate Thursday night he can defeat President Barack Obama in 2012, adding it was laughable for his rivals to challenge his conservative credentials.
But challenge him they did, within seconds, when former Pennsylvania Sen. Rick Santorum recalled that as House speaker Gingrich had to contend with a "conservative revolution" from the ranks of Republican lawmakers.
Gingrich, Santorum and five other White House hopefuls met on a debate stage for the last time before Iowa's Jan. 3 caucuses kick off the selection of delegates to next summer's Republican National Convention.
That made the stakes high, and Gingrich and Santorum were not the only ones eager to impress the television audience with their grit and conservative beliefs.
"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.
Former Massachusetts Gov. Mitt Romney, who runs second to Gingrich in the polls in Iowa, said his experience in private business made him the man to confront Obama in debates in the fall of 2012. "And I'll have credibility on the economy when he doesn't," he said.
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.
Iowa Gov. Terry Branstad, a Republican who has said he probably will not endorse a candidate before the caucuses, said Thursday that Gingrich needs to show he has discipline in the debate and 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."
Branstad described the debate as critical for Gingrich to show poise, but he said the final days leading up to the Jan. 3 caucuses would be a bigger test.
"I think it's volatile, that you could see big numbers switch," he said. "External factors can have an impact, and how well the candidates handle them will matter."
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."