"You can sense that it's going our way," Romney told reporters. The former Massachusetts governor was already looking ahead, making plans to stop in Minnesota on his way to Nevada on Wednesday, the day after Florida votes.
A day before the voting, Romney ridiculed Gingrich, his chief rival here: "Send him to the moon," Romney said at a rally early Monday, poking fun at Gingrich's claim to build a moon colony as president. Romney also scoffed at "the idea of the moon as the 51st state" as "not one that's come to my mind."
Gingrich countered that Romney is "pretending he's somebody he's not." Gingrich's allies, meanwhile, urged Rick Santorum to get out of the race to clear the way for conservatives to consolidate support behind the former House speaker.
In the final hours before Tuesday's critical primary, Romney sustained his barrage against Gingrich. He said he believes he bounced back from a tough South Carolina loss by aggressively answering Gingrich's attacks and hitting him for his ties to the government-backed, mortgage giant Freddie Mac.
Gingrich threatened a long slog. "I think he's going to find this a long campaign," Gingrich said.
"That's why they're trying to carpet-bomb us here in Florida," said former Gingrich aide Rick Tyler, who runs the pro-Gingrich political action committee Winning Our Future. "They're trying to end this thing. But it's not going to end."
Tyler visited the first of three rallies Romney had planned Monday to rail against Romney and urge Santorum to leave the race.
"I'm here to get as many cameras and microphones so I can talk about Mitt Romney's incessant failure to tell the truth," Tyler said, echoing Gingrich's recent claims about Romney's character. Tyler called Romney "despicable" and "disgraceful."
He also called on Santorum to leave the race to clear the way for Gingrich. "I think it would give us Mitt Romney, and I think Rick would hurt himself" by staying in, Tyler said.
Speaking to reporters, Romney said Gingrich's threats indicated desperation. "That's usually not a good sign," he said. "Everybody has a right to stay in as long as they think" they should, Romney said.
Gingrich kept up his attacks, saying Monday that on the big, philosophical issues, Romney "is for all practical purposes a liberal. I am a conservative."
"It's closing here in Florida," Gingrich said, "and I think the next 24 hours in going to make a big difference."
Polls showed Romney running ahead of Gingrich in the state. Romney earned positive reviews after two debates last week and has put the former House speaker on the defensive over his ethics and ties to Freddie Mac.
But instead of stepping back and refocusing on President Barack Obama - as he did in Iowa when it became clear that Gingrich had lost - Romney is ratcheting up his rhetoric and attacking until the very end. He hopes to close the Florida campaign strongly to push Gingrich as far back as possible.
Gingrich said Monday he was closing the gap with Romney in Florida. He said the Republican Party needed a "clear conservative" to run against Obama in the fall, and that there was very little difference between Obama and Romney when it came to their policies and politics, such as health care.
"Mitt Romney will have a very, very hard time trying to differentiate himself," Gingrich said.
Aides say Romney's attacks are partially a response to increasingly angry rhetoric from Gingrich, who on Sunday called the former Massachusetts governor "somebody who is a pro-abortion, pro-gun-control, pro-tax-increase liberal." Gingrich also accused Romney of lying. "I don't know how you debate a person with civility if they're prepared to say things that are just plain factually false," Gingrich said.
Romney's campaign responded immediately Sunday, starting with the candidate and continuing with statements from top surrogates who cast Gingrich's assault as an unfair attack on Romney's character.
"Mitt Romney is man of impeccable character," said New Jersey Gov. Chris Christie. "It offends me that Newt Gingrich would attack the character of Mitt Romney."
Former Minnesota Gov. Tim Pawlenty called the attacks "over the line."
In what has become a wildly unpredictable race, the momentum has swung back to Romney, who was staggered by Gingrich's victory in South Carolina on Jan. 21. Romney has begun advertising in Nevada ahead of caucuses there next Saturday, illustrating the challenge ahead for Gingrich.
An NBC News/Marist poll published Sunday showed Romney with support from 42 percent of likely Florida primary voters, compared with 27 percent for Gingrich.
Santorum, trailing in Florida by a wide margin, skipped campaigning to be with his 3-year-old daughter, Bella, who was hospitalized. He planned a pair of campaign appearances in Missouri on Monday.
Texas Rep. Ron Paul, who has invested little in Florida, also looked to Nevada. The libertarian-leaning Paul is focusing more on gathering delegates in caucus states, where it's less expensive to campaign. But securing the nomination only through caucus states is a hard task.