ORLANDO, Fla. — He drinks milk, not beer, and his vocabulary includes “gee” and “darn,” but Mitt Romney is being forced by increasingly tenuous political circumstances to show his mean guy.
Needing to convince Republican voters before the Florida primary on Tuesday that Newt Gingrich is an unacceptable option as the party’s presidential nominee, Mr. Romney is increasingly carrying out the attack himself.
It is hardly his first foray onto the dark side, but it is the most intense of his political career and a particular challenge for a candidate whose demeanor has been defined largely by caution and a can-do, problem-solving attitude.
Since his loss in the South Carolina primary on Saturday, Mr. Romney and his aides have carefully planned lines of attack that have emptied their opposition research file against Mr. Gingrich and put Mr. Romney in the midst of a highly personal battle in which he is no longer relying on advertising by an outside group to take the toughest shots at his opponent.
Mr. Romney is now fully participating in his campaign’s efforts to attack Mr. Gingrich’s morals and raise doubts about his emotional stability. Whether he can be withering enough without turning off voters or will appear too politically calculated is one of the biggest tests so far of his skills as a candidate.
Senior aides said their analysis of the campaign’s 10 days in South Carolina concluded that Mr. Gingrich did best when he went unchallenged, especially in debates. Coming into Florida, Mr. Romney’s advisers made two changes: increase their candidate’s aggressive talk and shift from rallies to events that would better drive their daily message.
In particular, they decided that Mr. Romney should seize on questions about Mr. Gingrich’s personal integrity, given his work as a highly paid consultant for Freddie Mac, the government-sponsored mortgage giant, and the ethics charges that he faced as speaker of the House.
At an event on Tuesday, Mr. Romney repeatedly called Mr. Gingrich an “influence peddler.” During the Monday debate, Mr. Romney said Mr. Gingrich had resigned his speakership “in disgrace.” And all week he has called Mr. Gingrich “erratic” and has hinted that he might be guilty of breaking conflict-of-interest laws. “You can call it whatever you like — I call it influence peddling. It is not right. It is not right,” Mr. Romney said directly to Mr. Gingrich. “You have a conflict. You are being paid by companies at the same time you’re encouraging people to pass legislation which is in their favor.”
Mr. Gingrich has painted Mr. Romney’s attacks as desperate and riddled with inaccuracies. But no one has ever accused Mr. Romney of not being tough. In 1994, he ran against Senator Edward M. Kennedy in a Massachusetts race that was anything but dainty. And in his 2008 bid for the presidential nomination, Mr. Romney clashed with his rivals, especially Senator John McCain.
But even when attacking, Mr. Romney stuck mostly to issues. His current willingness to bring up character is especially striking for a candidate who began his second presidential bid hoping to coast lightly over the nominating contest raging beneath him, while reserving his toughest language for President Obama.
The “old” Mr. Romney deplored personal attacks; the “new” one flings them with alacrity. The “old” Mr. Romney would go weeks without a mention of his Republican rivals; the “new” one bounces between biting critiques of the president and Mr. Gingrich.
“I would say there was a certain delight in it,” Stuart Stevens, a top aide to Mr. Romney, said after his sharp-edged debate performance. “I think Mitt Romney’s a very aggressive individual. You don’t succeed at the levels that he’s succeeded in his life, against pretty tough odds, without being aggressive.”
The new approach reflects what some Republican voters apparently want — a candidate who will engage Mr. Obama in a rhetorical death match. The audience reaction to Mr. Gingrich’s debate performances have proven how effective anger can be.
But Mr. Romney must find a way to project the anger that Republican activists want without turning off voters whom he will need in November — independents, women and suburban Republicans — if he becomes the nominee.
“I think he has a style of aggression that wears well, that’s not a bullying style,” Mr. Stevens said.
But other Republicans have noticed, and they are worried. Karl Rove on Wednesday called on both candidates to “step back” from the personal attacks in the face of polling that shows their negatives rising quickly.
“Stop! Stop!” Mr. Rove said to them on Fox News. “Have disagreements but realize that you’re only doing damage to your chances for the general election.”
And Mr. McCain, a Romney supporter, said the debates were “deteriorating, obviously, into serious personal attacks.”
But at least for now, the attacks continue. Standing in front of a foreclosed home in Lehigh Acres, Fla., Mr. Romney questioned Mr. Gingrich’s basic integrity, suggesting that Mr. Gingrich was for sale to the highest bidder.
“You get paid and then you go out and say things that influence other people,” Mr. Romney said of Mr. Gingrich.
That suggestion, in particular, has gotten under Mr. Gingrich’s skin. In debates, he has bristled at Mr. Romney’s suggestion that his advocacy was the result of a paycheck, not his core beliefs.
“It is not correct to describe public citizenship, having public advocacy as lobbying,” Mr. Gingrich said. “Every citizen has the right to do that.”