Ames, Iowa (CNN) - Long simmering tensions between Minnesota Rep. Michele Bachmann and former Minnesota Gov. Tim Pawlenty boiled over Thursday during a Republican presidential debate in Iowa, as the two candidates engaged in a harsh back and forth over their White House qualifications.
Mitt Romney, meanwhile, faced questions about the universal health care plan he enacted as governor of Massachusetts, but for the second debate in a row, the Republican frontrunner escaped without suffering a campaign-altering blow.
The nationally televised forum, sponsored by Fox News and The Washington Examiner and held in an arena at Iowa State University, took place only hours after news broke that Texas Gov. Rick Perry plans to officially join the presidential fray on Saturday.
With a respectable jobs record, deeply-held Christian beliefs and an ability to raise millions for his campaign, Perry has the potential to fundamentally alter the shape of the Republican race.
The eight candidates on stage - Romney, Pawlenty, Bachmann, former Utah Gov. Jon Huntsman, former House Speaker Newt Gingrich, former Pennsylvania Sen. Rick Santorum, Texas Rep. Ron Paul and businessman Herman Cain - were largely complimentary when questioned about Perry.
The kind words were a departure from a series of sharp exchanges between Bachmann and Pawlenty that dominated the first half of the debate.
Pawlenty, a former two-term governor, said Bachmann's record in the House is "non-existent."
"She has said she has a titanium spine," Pawlenty said. "It's not her spine we are worried about, it's her record of results."
He went on, calling her an ineffective member of Congress, naming several laws that President Barack Obama and Democrats have passed since taking 2009.
"If that's your view of effective results, please stop," Pawlenty said. "You're killing us."
A stone-faced Bachmann shot back, accusing Pawlenty of having abandoned his conservative principles while serving in St. Paul.
She said he supported a cap-and-trade plan to cut carbon emissions and once expressing support for a mandate that individuals purchase health insurance, though neither idea became law during his administration.
"That sounds a lot more like Barack Obama if you ask me," Bachmann said.
The two Republicans have engaged in long-distance sniping for weeks as both have raced across the state hunting for votes ahead of the potentially pivotal Ames Straw Poll on Saturday.
Bachmann has surged to the front of Iowa polls by appealing to a coalition of tea party activists and social conservatives, while Pawlenty has struggled to gain traction despite staking his campaign on a strong showing in the caucuses, the opening act of the 2012 Republican nomination fight.
Pawlenty's aggressive posture was an eye-opening departure from the last Republican debate in June, when he shied away from attacking his opponents, subsequently raising questions about his toughness and ability to take on President Obama in a general election.
His performance Thursday was an acknowledgment that his campaign needs to do more to raise doubts about his rivals if he hopes to boost his standing among Republican voters and donors.
After his full court press against Bachmann, Pawlenty pivoted to Romney and highlighted the similarities between the Massachusetts health care law and the one President Obama passed in 2009.
"We are going to have to take it to Barack Obama," Pawlenty said. "We have to show contrasts not similarities."
But Romney dismissed the charge and offered a familiar response, arguing that his health care law was right for Massachusetts and appropriate under the Tenth Amendment that reserves powers not granted under the Constitution to the states.
He called the health care law signed by President Obama a federal takeover and said that as president he would grant states health care waivers.
Later in the debate, Santorum and Paul battled over foreign policy and what they would do about Iran if elected to the White House.
Paul, a libertarian and longtime critic of American efforts overseas, said the United States should engage in diplomacy with Iran.
That prompted a fiery response from Santorum, who has long advocated for regime change in Iran. He told Paul that Americans should be wary of the Iranian nuclear threat.
"Anyone that suggests that Iran is not a threat to this country or is not a threat to stability in the Middle East is obviously not seeing the world very clearly," he said, jumping at the chance to highlight his foreign policy record from his time in the Senate.
Santorum, also a staunch social conservative, raised eyebrows by criticizing Iran's treatment of gays.
The regime, he said, "tramples the rights of women, tramples the rights of gays, tramples the rights of people all throughout their society."
Gingrich won applause with a punchy performance laced with attacks against the media, including the debate hosts.
He accused one debate moderator, Fox News host Bret Baier, of asking "gotcha questions."
The national media is obsessed with political process rather than "basic ideas that distinguish us from Barack Obama," he said.
The debate also presented Huntsman, who returned from his post as ambassador to China in April, with his first chance to address a national audience.
He avoided criticizing his rivals and instead set his sights on introducing himself to voters, touting his record of cutting taxes and fostering a strong business climate in Utah, which had a AAA bond rating during his tenure.
"When you look at me and you ask, 'What is that guy going to do?', look at what I did as governor," Huntsman said.