Matt Rourke, Associated Press
Republican presidential candidate, former House Speaker Newt Gingrich speaks at The River Church, Monday, Jan. 23, 2012, in Tampa, Fla.

TAMPA, Fla. — Republican presidential candidate Mitt Romney is launching a multipronged attack on rival Newt Gingrich, accusing the former House speaker of engaging in "potentially wrongful activity" in his consulting work.

As the Republicans campaign in Florida, Gingrich is dismissing Romney's criticism as desperate in the wake of a big loss in South Carolina.

Romney on Monday called on Gingrich to release the list of clients he helped after leaving Congress. He's offering no proof that Gingrich engaged in wrongful behavior when, after resigning from the House, he worked with former colleagues to push for a prescription drug benefit for Medicare. Gingrich has never been a registered lobbyist.

Gingrich says Romney is willing to "say almost anything" because the GOP nomination is beginning to "slip away" from the former Massachusetts governor.