Mitt Romney romped to a blowout victory in Florida's Republican U.S. presidential primary on Tuesday that put him back in front in the fight for his party's nomination to face President Barack Obama and left chief rival Newt Gingrich reeling but vowing to fight on.

With nearly all returns counted, Romney won 46 percent of the vote to Gingrich's 32 percent in the largest and most diverse of the four states to hold Republican presidential nominating contests so far this year.

Romney, the wealthy former Massachusetts governor and private equity firm executive, bounced back impressively from his decisive loss to Gingrich in the January 21 South Carolina primary.

The victory put Romney back on top in the race for the Republican nomination to face Obama, a Democrat, in the November 6 election. But it came at a cost.

His team spent millions of dollars on mud-slinging TV ads that lampooned Gingrich, raising new doubts about whether Romney can win hearts and minds rather than triumphing by tearing down opponents. Political organizations known as Super PACs, legally independent from the individual candidates, also poured money into advertising in Florida, adding to the negativity of the contest.

The bitter battle in Florida highlighted the deep divisions in a Republican Party struggling to remake its brand. Establishment Republicans back Romney and conservative voters favour Gingrich, a dynamic that could complicate the party's effort to derail Obama's re-election bid in November.

The intensely personal attacks also took the focus off of what is expected to be the biggest issue in this election and Obama's most vulnerable flank - the weak economy. Florida, with its 9.9 percent unemployment rate and home foreclosure crisis, was a stark reminder of a nation still reeling from its worst economic crisis since the Great Depression of the 1930s.

But Romney was quick to turn his attack mode back on Obama in a victory speech before jubilant supporters.

Leadership is about taking responsibility, not making excuses, said Romney. Mr. President, you were elected to lead, you chose to follow, and now it's time for you to get out of the way!

He waved away concerns about whether the tough battle between him and his Republican rivals will leave the party divided and easily beatable by Obama.

As this primary unfolds, our opponents in the other party have been watching, and they like to comfort themselves with the thought that a competitive campaign will leave us divided and weak, Romney said.

But I've got news for them. A competitive primary does not divide us. It prepares us, and we will win, Romney added. And when we gather here in Tampa seven months from now for our convention, ours will be a united party with a winning ticket for America.

But rival Rick Santorum, who won in Iowa but finished behind Gingrich on Tuesday night, decried the negative tone in Florida and said the Republican campaign should be about one thing: beating Obama.

We're not going to do that by mudslinging, he said in Las Vegas. If there's one message that I think we got from the campaign in Florida is that Republicans can do better.

Gingrich, a former speaker of the U.S. House of Representatives, vowed the fight has only just begun as he spoke in Orlando to supporters who waved signs that said, 46 states to go.

His pledge risks a divisive, months-long fight. He wants to keep going all the way until Republicans hold their convention to nominate their candidate in late August, a battle he pledges will be for the heart and soul of the conservative movement.


It is now clear that this will be a two-person race between the conservative leader Newt Gingrich and the Massachusetts moderate, Gingrich said, who did not publicly congratulate Romney for his victory.

Despite Gingrich's brave talk, the campaign for the Republican presidential nomination now tilts in Romney's favour with seven contests in February in which he could win or do well.

The next contest is the Nevada caucuses on Saturday, followed next Tuesday by caucuses in Colorado and Minnesota and a primary in Missouri.

The Florida primary was the fourth in the series of state-by-state contests to pick the Republican nominee. Romney has triumphed in two of the first four contests, having also won in New Hampshire and coming in second in Iowa and South Carolina.

While he performed well in two debates, his win may most be remembered for negativity. Romney's attack ads focused on ethics troubles that Gingrich experienced as House speaker and undermined Gingrich's argument that he is the conservative heir to Republican former President Ronald Reagan.

Gingrich fought back with ads of his own, castigating Romney as a party insider and elite friend of Wall Street - and called him for all practical purposes a liberal. But Gingrich did not have the same amount of money as Romney, who had used a similar advertising spree to cut Gingrich down to size in Iowa.


I think both of them are damaged by this dogfight in Florida, veteran Republican strategist Ed Rollins said of Romney and Gingrich. I've never seen anything quite like it in a presidential campaign.

Winning Florida demonstrated Romney's ability to compete strongly in a major political battleground state with a broad voter base that includes a diverse electorate including Tea Party conservatives, evangelical Christians and Cuban-Americans.

I voted for Romney. I think he'll create jobs, said Dino De Cicco, 38, of Melbourne Beach.

But the Florida campaign revealed that Republicans still hold doubts about Romney. Conservatives feel he has flip-flopped on some major issues and lacks a spine.

Romney is not a conservative, said Richard Jeske, 66, an Orlando security guard who voted for Gingrich.

These are concerns that Gingrich hopes to take advantage of as he tries to hang on until March when a number of Southern states vote. But if the Florida outcome is any proof, Gingrich may have some trouble in that regard.

In a sign that conservatives might be coalescing around Romney, 41 percent of people who said they supported the Tea Party voted for him, 4 percentage points more than those who voted for Gingrich, according to exit polls from Tuesday's vote.

According to exit polls by CBS, 62 percent of the Republican voters said the economy was the most important issue to them. Romney has campaigned hard saying he is best placed to fix the economy based on his experience as a businessman.

(Romney's) a businessman. He knows how to make money. If he makes promises, he'll keep them, said Frank Lobue, a retired utility company employee, who voted in St. Petersburg.

(Additional reporting by Ros Krasny, Sam Youngman, Jane Sutton and David Adams; editing by Mary Milliken and Will Dunham)