With his resounding victory over Newt Gingrich in Florida on Tuesday, Mitt Romney showed a worried Republican base a side of himself that it has both longed for and feared that he lacked: the agile political street fighter, willing to mock, scold and ultimately eviscerate his opponent.

But if he has quelled doubts about his toughness, he also emerges from the Florida free-for-all and the three contests that preceded it carrying heavy new baggage.

Mr. Romney was savaged by Mr. Gingrich over his record at Bain Capital, softening him up for the coming Democratic effort to portray him as a heartless capitalist happy to fire people to enrich himself. His release of his tax returns, complete with details about a Swiss bank account, provided new facts for opponents seeking to cast him as out of touch with ordinary Americans.

And the very trait that propelled him in Florida — a willingness to descend into the muck and run a relentlessly negative campaign — distracted from his economic-themed argument against Mr. Obama while deepening his rift with some populist conservatives. Should Mr. Gingrich remain a viable enough candidate to stay in the race through the summer, as he vowed on Tuesday, Mr. Romney could be forced to maintain an angry edge that could undermine his appeal among moderate and independent voters — groups whose views of him, polls suggest, appear to have been harmed by the Florida melee.