In a portion of the debate about the economy, Romney tried to disarm Gingrich by arguing that the former House speaker didn't have as big of a role in creating jobs during Congress as he has claimed. Romney's secret weapon was the diary of Ronald Reagan, the hero of the Republican Party.
"I looked at the Reagan diary. You're mentioned once in Ronald Reagan's diary," Romney said. "And in his diary, he says you had an idea in a meeting of young congressmen, and it wasn't even a very good idea."
Gingrich fired back later in the debate by trying to trap Romney on his positions on abortion, an issue that a so-called super PAC supporting Gingrich has raised in South Carolina in an effort to sway religious voters. Gingrich cited a litany of provisions in Romney's Massachusetts health care law that he said allowed tax-funded abortions, even after Romney had supposedly adopted an anti-abortion stance.
"If you're genuinely pro-life, how come these things are appearing?" Gingrich said.
Romney's response was that he's a "pro-life individual" whose integrity shouldn't be questioned.
The candidates also got heated while discussing health care, an issue that has taken a back seat to other matters during the campaign. Santorum led the charge against Romney as he lambasted "RomneyCare" for being the starting point for Obama's health care program that is hated among many Republicans.
Bluntly, Santorum, 53, said Romney's health care plan that was put in place in Massachusetts was the model that Obama used.
"He's going to have run against a president who's going to say: 'Well, look. Look at what you did for Massachusetts, and you're the one criticizing me? ... I used your model for it.'"
While the crowd responded warmly, signaling many conservatives' hesitance to embrace Romney, the former Massachusetts governor said his plan was "absolutely not" perfect but that "having been there, having been on the front lines," he'd know how to repeal Obama's plan.
Santorum didn't buy it. "You do not draw a distinction that's going to be effective for us, just because it was at the state level, not the federal level," he said.
But Santorum also didn't save his criticism just for Romney. He accused Gingrich of being late to back off his stance on the individual mandate, and he later argued that Gingrich would be a dangerous Republican nominee because he's unpredictable. As an example, Santorum cited Gingrich's comment that Santorum should drop out of the GOP race, even though the former Pennsylvania senator beat him in Iowa and in New Hampshire.