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. The victory, his 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 this time as he rebounded from a stinging double-digit loss to Gingrich in South Carolina 10 days before.

Before a jubilant audience in Tampa, Romney used his victory speech to take aim at President 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 will 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.”

Gingrich, who appeared in Orlando, did not congratulate Romney on his victory. Instead, standing before supporters holding placards that read “46 states to go,” he vowed to keep fighting for the nomination. “We are going to contest every place, and we’re going to win, and we will be in Tampa as the nominee in August,” he said.

The former House speaker noted the imbalance in spending between his campaign and Romney’s in Florida but said he would depend on people power to defeat money power. And he issued a direct appeal to voters who want to shake up Washington: “We believe it is cheating our grandchildren to not insist on fundamental, basic change in Washington, even if the establishment doesn’t like it.”

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. February, which includes five contests, will play out on terrain highly favorable to Romney. That leaves Gingrich with the challenge of trying to consolidate the conservative vote if he is to revive his candidacy for a third time in this 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 after the final polls closed Tuesday night. Romney led Gingrich by double digits. Former senator Rick Santorum (Pa.), who had to break off campaigning after his daughter Bella was hospitalized over the weekend, was a distant third. Rep. Ron Paul (Tex.), who did not really contest the state, ran fourth.

Santorum, already in Nevada on Tuesday night, said the Florida results should be an indicator that Gingrich cannot coalesce the conservative vote, and he predicted that conservatives will turn to him to try to stop Romney. “Newt Gingrich had his chance, had his shot . . . and couldn’t deliver in Florida,” he said in an interview on CNN.

Paul, who also was in Nevada, was undeterred by his second straight fourth-place finish. He, too, said he will continue his quest, with special emphasis on states with caucuses, rather than primaries, where his organizational strength and passionate supporters can have a greater influence on the outcome.

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 the other. 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 were negative attacks aimed at Gingrich.

By the time Gingrich 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 by the former speaker, according to CMAG figures. Gingrich never got 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 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 exit polls showed Romney dividing those voters with Gingrich and winning the majority who said they were not born-again Christians, along with 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 the ability to defeat 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 the other. 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.

Polling director Jon Cohen in Washington contributed to this report.