Key moments in Saturday night's Republican presidential debate:

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IRAN:

Former Massachusetts Gov. Mitt Romney warned that only his administration could prevent Iran from obtaining a nuclear weapon.

"If we re-elect Barack Obama, Iran will have a nuclear weapon," Romney said. "And if we elect Mitt Romney, if you'd like me as the next president, they will not have a nuclear weapon."

Herman Cain said he supports regime change in Iran, but stopped short of threatening military action. He favors moving warships to the region to deter Iran and would support the resistance to Tehran to overthrow the regime.

Texas Gov. Rick Perry said America should sanction the Iranian central bank to "shut down that country's economy. And that's what the president needs to do."

And rival Ron Paul, a congressman from Texas, says any use of force against Iran would require approval from Congress.

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PERRY'S GAFFE:

Perry poked fun at himself again for forgetting about the Department of Energy during the last debate when he tried to name the three agencies he'd cut.

On this night, Perry said he was glad that moderator Scott Pelley of CBS News remembered to ask him about the Energy Department. The moderator said he's had some time to think about it.

"Me too," Perry cracked back, drawing laughs from the knowing audience.

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DON'T BAIT NEWT:

Former House Speaker Newt Gingrich _ who is rising in polls _ refused to take the bait when asked to evaluate former Massachusetts Gov. Mitt Romney, who leads the GOP field in polls.

"No," Gingrich said.

When the moderator noted that Gingrich had been willing to criticize Romney the night before, Gingrich responded: "Yesterday, I was on a national radio show."

He took a pass on this night, adding: "We're here tonight talking about how every one of us is better than President Obama."

Gingrich called Romney "a friend who's a great businessman" and "a great improvement over Obama."

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HOME STATE SENATORS:

Toward the end of the debate, South Carolina's junior and senior U.S. senator took over the questioning _ and used the opportunity to raise their pet issues.

Sen. Lindsay Graham pressed the candidates on the prison for terror suspects at Guantanamo Bay, Cuba, as well as on interrogation techniques and military tribunals _ topics he's long worked on in the Senate.

Sen. Jim DeMint asked the candidates what programs they'd cut to bring down the debt _ perhaps the top issue among fans of the tea party.

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WHAT YOU DIDN'T SEE ON TV:

As the debate began, someone shouted: "The military loves Ron Paul!"

Mark Sanford, the former South Carolina governor who left office in disgrace after acknowledging an affair with an Argentine woman, was on hand.

Gingrich got a strong reaction from the crowd with one word: "No." He refused to criticize Romney in front of this audience as he did earlier this week in questioning Romney's ability to think outside the box.