TRENTON — Gov. Chris Christie went on full attack-dog mode Sunday, calling Republican presidential candidate Newt Gingrich an "embarrassment for the party" on national television hours after the former House speaker defeated Mitt Romney in the South Carolina primary.



"I'm not talking about character, I'm talking about how you conducted yourself in office," Christie said on "Meet the Press" on NBC. "Newt Gingrich has embarrassed the party over time -- whether he'll do it again in the future, I don't know."



Christie, who declined to run for president in October despite a tidal wave of encouragement, has since become a top surrogate for Romney on the campaign trail, raising money, traveling to early-voting states and making the rounds on television for the former Massachusetts governor.



After a rocky start to his campaign, Gingrich won over 40 percent of South Carolina's Republican primary voters -- some of the most conservative in the country -- to Romney's 28 percent.



"It's clearly disappointing," said Christie. "We had a bad week as a campaign and a bad result last night."



But the governor said Romney would still end up the nominee. Florida, the next state to vote, could help Romney regain momentum after second-place finishes in South Carolina and in Iowa, where a recount last week bumped him down from first.



Romney, a multimillionaire, was also hammered last week for saying he pays an effective rate of 15 percent in income taxes. After heavy criticism and friendly advice from Christie and others, he agreed Sunday to release his tax returns on Tuesday.



Experts said Florida would have an outsize role deciding the GOP nominee, since the first three states have all gone for different candidates: Iowa for Rick Santorum, New Hampshire for Romney and South Carolina for Gingrich.



Ed Rollins, a top Republican strategist, told The Star-Ledger the straight-talking Christie would be a huge asset for Romney in Florida, "by far" more than Romney himself on the stump. A Quinnipiac poll of GOP primary voters in Florida earlier this month had Romney leading Gingrich 36 percent to 24 percent, but in December the same poll had Gingrich on top at 35 percent and Romney at 22 percent.

Daniel Smith, a political science professor at the University of Florida, said he expects Gingrich to move up in the next round of polls. But he added that Florida was still Romney's to lose and said Christie could be a powerful weapon.

"We have a lot of transplants here from New Jersey, New York," he said. "It's not like South Carolina."

Christie’s communications director, Maria Comella, said there weren't any plans as of Sunday for the governor -- who stumped for Romney in Iowa and New Hampshire but not South Carolina -- to hit the campaign trail in the Sunshine State.

Instead, Christie made the case for Romney on the airwaves. Only Romney has the business experience and governing chops to repair the U.S. economy, he said.



"Look at places like Staples and Sports Authority," Christie said, referencing Romney's work as a venture capitalist. "Everybody who goes to work at those places today has Mitt Romney to thank."



By contrast, Christie recapped a list of "liabilities" he said would hurt the Republican Party if Gingrich became the nominee.

He said the former speaker used his influence in Washington to earn $1.6 million consulting mortgage giant Freddie Mac, and now dresses it up on the campaign trail as the work of a "historian" or "strategic adviser."



Christie also pointed out that Gingrich was ousted as speaker by his own majority, and accrued a mountain of ethics violations costing $300,000 in fines.



"Sometimes past is prologue," Christie said.



Interviewed just moments before, Gingrich said South Carolina voters were angry with the national establishment and "are sick of being told what they're allowed to think and what they're allowed to say."



And later, his Florida campaign co-chairman, Alan Levine, told the Miami Herald that Christie's attacks were "disappointing."



"Far be it from me to tell the governor of New Jersey to focus on his own state, but this isn't a way to begin a campaign in Florida," he said, and quoted former Florida Gov. Jeb Bush's advice to Republicans from Saturday night: "'Stop the circular firing squad.'"



On "Meet the Press," when the conversation turned to the vice-presidential nomination, Christie again said it was unlikely he would join the Republican ticket, without fully closing the door.



"I don't know that I'm the guy to stand 3 feet behind someone and nod my head," Christie said. "(But) I love my country enough and I love my party enough to listen."



Christie said both Gingrich and President Obama are ill suited to the Oval Office because they have only served as lawmakers previously. When asked about electability, though, Christie conceded that Gingrich could defeat the president in November.



"You don't sound as convinced, though," said host David Gregory.



"I answered your question," Christie retorted. "Sure."

Jenna Portnoy contributed to this report.



Related coverage:

• Gingrich defeats Romney in upset South Carolina GOP primary