Key moments in Thursday night's GOP presidential debate:
A moderator asked Texas Gov. Rick Perry to explain how he would change Social Security _ and whether the plan could work if it was run by 50 states instead of the federal government. Former Massachusetts Gov. Mitt Romney has claimed that's what Perry wants to do.
Perry snapped back at Romney: "Now, it's not the first time that Mitt has been wrong on some issues."
Romney insisted again that Perry, in his book, "Fed Up!", says Social Security is unconstitutional and should be returned to the states. "So you better find that Rick Perry and get him to stop saying that," Romney said.
Perry had criticism of Romney's book, "No Apology," ready. In the hard copy, "you said it was exactly what the American people needed _ to have that RomneyCare given to them as you had in Massachusetts," Perry said, referring to the health plan Romney signed as governor. "Then in your paperback, you took that line out. So speaking of not getting it straight in your book, sir."
Other notable moments:
_ Perry also staunchly defended his immigration record in Texas _ he signed a bill allowing the children of undocumented immigrants to receive in-state tuition at public Texas universities: "The fact of the matter is this _ there is nobody on this stage who has spent more time working on border security than I have. For a decade I've been the governor of a state with a 1200-mile border with Mexico. We've put $400 million of our taxpayer money into securing that border," he said. "But if you say that we should not educate children who have come into our state for no other reason that they've been brought there, by no fault of their own, I don't think you have a heart."
_ Perry recalled the 2004 election, channeling President George W. Bush's attacks on Democratic nominee John Kerry, when he accused Romney of flip-flopping on a number of issues throughout his political career. "Americans just don't know what Mitt Romney they're dealing with," Perry said. "Is it the Mitt Romney that was against the second amendment before he was for the second amendment?"
_ Former New Mexico Gov. Gary Johnson won laughs when he put in a plug for some neighborhood dogs: "My next door neighbor's two dogs have created more shovel-ready jobs than this current administration."
_ In a "wild card" question, candidates were asked if they won the presidential nomination, which of their GOP presidential rivals would they choose as vice president.
Texas Gov. Rick Perry said he'd like to combine the qualities of former House Speaker Newt Gingrich and businessman Herman Cain. "If you could take Herman Cain and mate him up with Newt Gingrich, I think you would have a couple of really interesting guys to work with."
Massachusetts Gov. Mitt Romney responded, "there are couple of images I'm going to have a hard time getting out of my mind. That's one, and Gary Johnson's dogs are the other."
_ "Not an inch, sir." _ Perry responding to Romney's accusations that Perry is retreating from claims made in his book.
_ "There are a lot of reasons not to elect me. There are a lot of reasons not to elect other people on this stage. But one reason to elect me is that I know what I stand for. I've written it down. Words have meaning, and I have the experience to get this country going again." _ Romney claiming he has stood by the positions outlined in his book.
_ "I don't plan to make a choice at the moment because I am, in national polls, it seems like I'm in third place now...as soon as I'm one of the two top tier then I will start thinking along that line." _ Texas Rep. Ron Paul's explanation of why he would not select a vice presidential nominee from the debate stage.
_ A YouTube question from Stephen Hill, a soldier serving in Iraq, generated some boos from the audience when he asked if the candidates would "circumvent the progress that has been made for gay and lesbian soldiers in the military." The audience cheered former Pennsylvania Sen. Rick Santorum, who said he would reinstate the "Don't Ask, Don't Tell" policy and opposed social experimentation with the military. "Keep it to yourself whether you're heterosexual or homosexual."
_ Moderators asked all the candidates to choose a vice presidential nominee off of the debate stage _ and Perry decided he wanted both Newt Gingrich and Herman Cain. "If you could take Herman Cain and marry him up with Newt Gingrich, I think you would have a couple of really interesting (people)," Perry said.
_ Former New Mexico Gov. Gary Johnson won laughs from the Republican field when he put in a plug in for some neighborhood dogs: "My next door neighbor's two dogs have created more shovel-ready jobs than this current administration."