In a debate that's already been fiery, the temperature rose further, even a little uncomfortably, when the subject of immigration came up.
The candidates on this stage have repeatedly said they won't elaborate on their plans for dealing with the 11 million to 12 million illegal immigrants already in the country until the border with Mexico is secured.
Perry, who signed a Texas version of the DREAM Act (which allows young people in the country illegally to pay in-state tuition at public colleges and universities) drew several rounds of boos when he defended the policy.
"If you've been in the state of Texas for three years, and working toward citizenship, you pay in-state tuition," said Perry. "It doesn't matter what the sound of your last name is. That's the American way."
The point, he said several times, is to allow immigrants to become "contributing members of our society, rather than be on the dole."
As he has often done, Perry reiterated this evening that he does not believe a fence along the entire border is feasible.
"The idea you're going to build a wall from Brownsville to El Paso and go left to Tijuana is not reality," said Perry to booing. "What you gotta have is boots on the ground … the aviation assets in the air. We understand and know how to secure that border, but the federal government needs to step up and do their constitutional duty and secure the border with Mexico."
Huntsman, who has tried repeatedly to get traction with sarcasm or over-the-top statements tonight, seemed to stun the audience when he said, "For Rick to say you can't secure the border is pretty much a treasonous comment. We can secure the border." (Huntsman was alluding to Perry's controversial remark that Fed Chairman Ben Bernanke's policies amount to treason.)
Romney piled on Perry (a recurring theme of the evening).
"Of course we build a fence, and of course we do not give in-state tuition credits to people who have come here illegally."
And then he took the opportunity to knock Huntsman, who, while Utah governor, allowed illegal immigrants to have driver's licenses (though the documents were not to be used as a form of legal identification).
"This is the party that believes in supporting the law," Romney said to Huntsman.
Huntsman was having none of it: "We can spend all night talking about where Mitt's been on the issues and that would take forever."