Confident Romney looks for big win in Fla.

Newt Gingrich and Mitt Romney

As voters cast their ballots in Florida's Republican presidential primary on Tuesday, polls show Mitt Romney with a commanding lead over his nearest competitor, Newt Gingrich.

The latest numbers show Romney ahead of Gingrich by 20 points.

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It's hard to believe that, just a week ago, Romney was coming to the Sunshine State on the ropes after Gingrich beat him in South Carolina. Now, the question isn't who is going to win, it's how much Romney will win by.

Romney sounded so confident Monday that he mocked the former House speaker: "I know the speaker is not real happy," he said. "Speaker Gingrich -- he's not feeling very excited these days." The crowd let out a collective aww. "I know," Romney said. "It's sad." (Click the player at left to see Romney's remarks

Despite plummeting in the polls, Gingrich continued to hammer Romney as too liberal to win, saying, "We nominated a moderate in 1996. He lost. We nominated a moderate in 2008, he lost. Mitt Romney is more liberal than either of those candidates."

Gingrich blasts "liberal" Mitt, GOP establishment

But win or lose, Gingrich is vowing to stay in the race until the end, saying he'll be in Tampa (Fla.) in August at the Republican Convention. "Why would anybody in the establishment," Gingrich asked, "think that a Massachusetts moderate (Romney is a former Massachusetts governor), which is a liberal by Republican standards -- pro-abortion, pro-gun control, pro-tax increase, pro-gay rights -- why would they think he's going to be able to debate Barack Obama?"

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Talking with reporters on his campaign plane, a relaxed Romney dismissed Gingrich's remarks, saying, "That's usually an indication that you think you're going to lose. When you say, 'I'm going to go on no matter what happens,' that's usually not a good sign."

After Florida, Romney is expected to do well in the next five contests - Nevada, Maine, Colorado and Minnesota hold caucuses, which require what Gingrich does not have: a substantial organization. And Gingrich isn't even on the ballot in Missouri.

And there are no more debates until Feb. 22 -- and debates had, until recently, been Gingrich's strongest suit.

The Romney campaign vows not to let up after Florida.

To see Jan Crawford's full report, click on the video in the player above.

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    Jan Crawford is CBS News Chief Legal Correspondent.