TAMPA, Fla. — Bolstered by superior resources and a relentlessly aggressive style, Mitt Romney won a decisive victory in the Florida primary Tuesday night, dealing a major setback to principal rival Newt Gingrich while putting himself back into a commanding position in the race for the Republican presidential nomination.

Romney’s win came after a bitter and almost wholly negative campaign by both leading candidates. His victory, the second of the year to go along with two defeats, gives the former Massachusetts governor much-needed momentum as the GOP contest moves west for Saturday’s Nevada caucuses. Romney is strongly favored to repeat his 2008 victory there.

Romney, whose defeat in Florida four years ago effectively ended his hopes of winning the nomination, attracted solid support across the Sunshine State and among key groups as he rebounded from a stinging double-digit loss to Gingrich in South Carolina 10 days ago.

Before a jubilant audience in Tampa, Romney used his victory speech to take aim at President Barack Obama and his record on the economy. ”Leadership is about taking responsibility, not making excuses,” he said. ”Mr. President, you were elected to lead. You chose to follow. Now it’s time for you to get out of the way.”

Romney also addressed the tone of the Florida campaign. Democrats, he said, may believe that the primary campaign would leave Republicans ”divided and weak.” ”A competitive primary does not divide us,” he said. ”It prepares us. 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.”

Long seen as a critical firewall among Romney’s top advisers, Florida became just that for a candidate whose wobbly performance in South Carolina opened the door to Gingrich’s resurgent candidacy.

Florida’s primary has once again altered the dynamic of the GOP race. The rest of February, which includes five more contests, will play out on terrain highly favorable to Romney. That leaves the former House speaker with the challenge of trying to consolidate the conservative vote if he is to revive his candidacy for a third time in the campaign.

The personal attacks that characterized the Florida campaign foreshadow a potentially long and divisive nomination battle, especially if Gingrich makes good on his vow to keep fighting for months.

Television networks called Romney’s victory almost immediately as the final polls closed Tuesday night. Romney led Gingrich by double digits. Former Sen. Rick Santorum of Pennsylvania, who had to break off campaigning after his daughter Bella was hospitalized over the weekend, was a distant third. Rep. Ron Paul of Texas, who did not really contest the state, ran fourth.

Gingrich’s South Carolina upset made Romney a far more aggressive candidate in Florida. Over the past 10 days, he and Gingrich traded increasingly harsh attacks from one end of the state to another. He also bested Gingrich in a pair of debates after losing both debates in South Carolina.

But what may have been even more critical to Romney’s success in Florida was the fact that he overwhelmed Gingrich on television in a state where TV commercials are both costly and necessary.

Romney and the super PAC backing him outspent Gingrich and his super PAC on television by at least 5 to 1, according to estimates. His campaign alone spent more than $11 million on television, compared with less than $2 million by Gingrich.

More than 90 percent of the ads aired in the state over the past 10 days were negative, according to Kantar Media’s Campaign Media Analysis Group (CMAG). Two-thirds of the ads aired were negative attacks aimed at Gingrich.

By the time he arrived in Florida after his South Carolina victory, Romney and his super PAC had already dropped more than $5 million into television commercials in the state, compared with virtually nothing for the former speaker, according to CMAG figures. Gingrich never could get out of that hole.

Florida’s voting patterns were sharply different from South Carolina’s, according to exit polls, with Romney shattering the coalition Gingrich put together in the Palmetto State. The contours of the vote here on Tuesday raise questions about whether the former speaker can reassemble the coalition that brought his success in South Carolina quickly enough to have a chance of winning the nomination.

Romney won a majority of female voters Tuesday and also led among men, a reversal from South Carolina. Romney easily carried Hispanic voters, a key constituency in the state. The former governor won among those with college degrees and those without. He won among all age groups.

Among Cuban Americans, Romney’s margin over Gingrich was approaching 2 to 1. Four years ago, he won just 9 percent of the Cuban American vote.

Gingrich’s hopes rested on his ability to win decisively among evangelical Christians and tea party supporters. But the exit polls showed Romney dividing those voters with Gingrich and winning the majority who said they were not born-again Christians and among those who said they were either neutral or opposed to the tea party.

Gingrich won among the most conservative voters in Florida, but Romney easily carried those who described themselves as ”somewhat conservative,” a group that often held the balance in GOP primaries four years ago. Among the six in 10 who said the economy was the most important issue in the election, Romney held a double-digit lead.

The attacks on Gingrich took a toll on his image. Nearly half the voters in the state said defeating Obama in November was the quality that was most important to their decision, and Romney trounced Gingrich with this group.

Romney had an even bigger margin among the one-sixth of the electorate that said their top priority was a candidate with strong moral character. Gingrich and Romney split the votes of those who said experience was the key quality in their decision.

Romney’s strength carried from one end of the state to another. He crushed Gingrich in South Florida, which he lost four years ago. He was running well across the crucial Interstate 4 corridor in the center of the state, which often holds the key to Republican hopes in general elections. He was doing even better along the southern Gulf Coast. In northern Florida, the most conservative area of the state, Romney and Gingrich were splitting the vote.

Gingrich arrived in Florida the day after South Carolina’s primary with considerable momentum, but almost immediately Romney began to turn the race around. In his first appearance in the state he hit Gingrich with a series of attacks, calling him a failed speaker whose ethics reprimand by the House was a major embarrassment.
He highlighted Gingrich’s work for housing giant Freddie Mac and contrasted his rival’s consulting fees with the homeowners in Florida who had been foreclosed in part because of the agency’s decisions.

After using the South Carolina debates to propel him to victory, Gingrich struggled through a pair of forums in Florida. On Jan. 23 in Tampa, he appeared off his game as Romney pressed the same attacks on stage that he had hammered Gingrich with on the campaign trail. He wasn’t helped by the fact that the audience, in contrast to most of the earlier debates, was urged to remain silent.

As the debate was ending, Romney put out his tax returns, after paying a political price for holding them back during South Carolina. They showed that he paid an effective tax rate of about 14 percent, that he and his wife, Ann, gave enormous amounts of money to charity, and that his finances included overseas holdings. Gingrich tried to make an issue of them, but the attacks never took hold.

Last Thursday, the candidates debated again. A combative Romney was relentless in going after Gingrich again. They quarreled over immigration. Romney said it was ”repulsive” for Gingrich to accuse him of being anti-immigrant. They argued over Romney’s finances, with the former governor issuing a strong statement defending his success in business. Romney ridiculed Gingrich’s proposal to put a permanent U.S. colony on the moon.

Adding to Gingrich’s problems in Florida was the pounding he took from the Republican establishment. Leading voices in the party elite piled on Gingrich, warning that he could put Republicans up and down the ticket at risk in the general election.

The former speaker tried to cast himself as the insurgent in the race and the heir to the legacy of former President Ronald Reagan. But he grew increasingly angry as the Florida campaign drew to a close. He said Romney’s attacks were ”breathtakingly dishonest,” labeled his rival a ”Massachusetts liberal” and vowed to carry his fight for the nomination all the way to the national convention, which will be held in Tampa in late August.

Gingrich won the endorsement of former candidate Herman Cain and called in Michael Reagan, a son of Reagan, for a final day of campaigning. But he failed to find a message for Floridians that could overcome the barrage of attacks from Romney and his supporters.