In a call last Sunday morning, just hours after Mr. Romney’s double-digit loss to Mr. Gingrich in the South Carolina primary, the Romney team outlined the new approach to the candidate. Put aside the more acute focus on President Obama and narrow in on Mr. Gingrich.

Find lines of attack that could goad Mr. Gingrich into angry responses and rally mainstream Republicans. Swarm Gingrich campaign events to rattle him. Have Mr. Romney drop his above-the-fray persona and carry the fight directly to his opponent, especially in two critical debates scheduled for the week.

The results of that strategy, carried out by a veteran squad of strategists and operatives assembled by Mr. Romney to deal with just this kind of moment, have been on striking display here.

By this weekend, Mr. Romney’s aides were on the offensive and increasingly confident, with some combination of their strategy and Mr. Gingrich’s own performance swinging polls in Mr. Romney’s direction. Even as it acknowledged the damage inflicted on Mr. Romney by the past several weeks, his team suggested that it had learned a lesson about never letting up on rivals, especially if Mr. Romney wins the nomination and confronts Mr. Obama in the general election.

On Saturday, Mr. Gingrich vowed to fight on to the Republican convention, backed by a well-financed “super PAC,” the enthusiasm of grass-roots conservatives and sympathetic statements from the likes of Sarah Palin, who in a Fox Business interview late last week said the “establishment” was trying to “crucify” Mr. Gingrich.

With the Florida primary two days away, Mr. Gingrich is now facing the full capabilities of a Romney team that was built for battle, but that by several accounts became so confident during primary season that it failed to see Mr. Gingrich’s latest resurgence coming, presuming that he had been left for dead in Iowa.

“We had a moment where we kind of started drinking our own Kool-Aid, and it looked like we were just going to blow through it,” said John D. Rood, a chairman of Mr. Romney’s Florida finance team. “There is a little humility in getting your butt kicked in South Carolina, and all of the sudden it’s a wake-up call.”

Behind the scenes, it was more than that. It was a call to arms employing all the visible and invisible tactics of political warfare. As recently as Wednesday, several Romney advisers, donors and supporters were speaking in terms of what losing in Florida would mean and how they could survive it.

If Mr. Romney does win here on Tuesday, it will have been through a blistering and unrelenting series of attacks. His campaign has pressed everything at its disposal into service to eviscerate Mr. Gingrich, painting him as an erratic, unreliable Washington insider in mailings and television advertisements, at two critical debates here (where his team made sure Mr. Romney had ample and vocal supporters in the audiences) and even by sending supporters to mock him at his own events.

On Saturday, it released a new ad featuring a 1997 NBC News segment in which the anchor Tom Brokaw reported that Congressional peers of Mr. Gingrich, then speaker of the House, had “found him guilty of ethics violations.”

David Kochel, an adviser who arrived here from Iowa to oversee the pressure campaign, described the strategy as “let’s go rush the quarterback.” A team of Romney boosters started infiltrating nearly every Gingrich campaign stop to offer instant rebuttals. Representative Jason Chaffetz of Utah showed up to challenge Mr. Gingrich’s record to reporters and at one point tangled with Mr. Gingrich’s press secretary as the cameras rolled. Bay Buchanan, a longtime conservative activist, worked on the Romney campaign’s behalf to win over voters and commentators.