Sioux City, Iowa (CNN) -- A Republican presidential race that has lately been defined by its negative tone took a sunnier turn Thursday, as the field of GOP candidates presented closing arguments to voters in the final debate before January's pivotal Iowa caucuses.
The sharp attacks between the GOP frontrunners that have played out in media interviews and television ads largely took a backseat in the Sioux City debate, which was sponsored by the Iowa Republican Party and Fox News.
Former Massachusetts Gov. Mitt Romney recently launched an all-out assault against his chief rival for the nomination, former House Speaker Newt Gingrich, openly questioning his temperament and conservative record.
But Romney took a pass on attacking Gingrich on Thursday, instead training his sights on President Barack Obama as he sought to portray himself as the most credible Republican choice for 2012.
"It's President Obama we ought to be talking about," Romney said. "He has unveiled himself as a president who is not the right person to lead this country."
Texas Gov. Rick Perry has also attacked Gingrich in television ads and on the campaign trail, but he, too, stayed above the fray and painted himself as a comeback kid.
Perry, attempting to mount a comeback in Iowa after an October collapse in the polls, compared himself to Tim Tebow, the often-underestimated Denver Broncos quarterback.
"There are a lot of folks out there who said Tim Tebow isn't going to be a good NFL quarterback," Perry said, displaying an energy that escaped him in previous debates. "Am I ready for the next level? Let me tell you, I am ready to be the Tim Tebow of the Iowa caucuses."
Sharing the stage were Texas Rep. Ron Paul, former Pennsylvania Sen. Rick Santorum, Minnesota Rep. Michele Bachmann and former Utah Gov. Jon Huntsman, who offered a stark vision for America if Obama remains in office for a second term.
"This nation has been downgraded," Huntsman said. "This nation is on the cusp of the third government shutdown. We have been kicked around as people. We are getting screwed as Americans."
Though Romney and Perry held their fire, debate moderators immediately shone a spotlight on Gingrich, the latest GOP frontrunner and the candidate who has mounted the most durable challenge to Mitt Romney.
Gingrich has been attacked by nearly every one of his Republican opponents, who have highlighted his past conservative apostasies, such as his past support for health insurance mandates and his collaboration with Nancy Pelosi on an anti-climate change initiative.
Asked about the attacks, Gingrich staunchly defended himself.
"It's sort of laughable to suggest that some someone who campaigned with Ronald Reagan and with Jack Kemp, and has a 30 year record of conservatism is somehow not conservative," he said.
Bachmann, one candidate who trails Gingrich in the polls but needs a top three finish in Iowa to survive, aggressively challenged the frontrunner's conservative credentials and attacked Gingrich for his association with Freddie Mac.
Gingrich earned $1.6 million advising the federally backed mortgage giant but has denied lobbying on its behalf.
Bachmann called Freddie Mac and Fannie Mae the "epicenter of the mortgage financial meltdown."
"You don't need to be within the technical definition of being a lobbyist to still be influence-peddling with senior Republicans in Washington, D.C. to get them to do your bidding," she said. "And the bidding was to keep this grandiose scam of Freddie Mac going. That is something that our nominee can't stand for."
Gingrich retorted that he "never lobbied under any circumstance."
"Sometimes people ought to have facts before they make wild allegations," he said.
Bachmann also engaged with a back-and-forth with Paul after the libertarian-leaning congressman advocated diplomacy with Iran instead of sanctions or possible military action to prevent the country from developing nuclear weapons.
Bachmann called that posture "dangerous" and said Iran could wipe out the state of Israel with a nuclear attack.
Santorum, meanwhile, took aim at Romney and accused him of supporting same-sex marriage as governor of Massachusetts.
Romney was governor when the state Supreme Court legalized same-sex marriage in 2003 but opposed the decision.
"He personally as governor issued gay marriage licenses," Santorum claimed.
Romney answered: "Let me tell you, I want to make it very clear, I have been a champion of protecting traditional marriage that continues to be my view."