Chief rival Mitt Romney sharpened his attacks on the former House speaker, calling him "erratic" and pressing for disclosure of clients, contracts, records and other work he was paid to do after leaving Congress. Atop Romney's list are Gingrich's consulting arrangements with mortgage giant Freddie Mac and details of ethics investigations in the 1990s.
Romney also charged that Gingrich had engaged in "potentially wrongful activity" when he worked with former colleagues in Congress to create a prescription drug benefit for Medicare.
"We could see an October surprise a day from Newt Gingrich," Romney said after a round-table session with people struggling with home foreclosure problems.
Gingrich, who earlier had appeared on ABC's "Good Morning America," mocked Romney as "somebody who has released none of his business records, who has decided to make a stand on transparency without being transparent." After initially balking, Romney is set to release personal tax records on Tuesday.
The sniping between the two contenders opened a Florida fight that is shaping up as pivotal to determining which one of them will become the GOP's presidential nominee. The four candidates - Gingrich, Romney, Rick Santorum and Ron Paul - were to meet Monday night in Tampa for the first of two debates heading into Florida's primary on Jan. 31.
Gingrich, who planned a pre-debate campaign appearance on Monday afternoon in Tampa, basked in his come-from-behind triumph in South Carolina two days earlier. The win made for three different winners in the first three states to hold contests, with Santorum winning Iowa and Romney taking New Hampshire.
Gingrich's campaign said it had raked in $1 million in the first 24 hours since South Carolina's primary Saturday.
Frequently the aggressor in the race, Gingrich is now the one taking fire from all sides.
Santorum described Gingrich as too "high risk" to be the Republican standard-bearer. Romney has been calling Gingrich a lobbyist. Gingrich flatly denied lobbying on behalf of Freddie Mac or other clients.
"It's not true. He knows it's not true. He's deliberately saying things he knows are false," Gingrich said. "I just think that's what the next week will be like."
Gingrich told ABC he has campaign lawyers working to make the Freddie Mac records public. He said the decision rests with the Center for Health Transformation, which he founded but no longer owns. Two former Gingrich companies earned $1.6 million over eight years from Freddie Mac. Gingrich has said he only earned about $35,000 a year himself.
Gingrich's work for Freddie Mac has come under scrutiny because of its role in the housing meltdown.
After the housing forum Monday, Romney told reporters that Gingrich should consider giving back any money he earned from the troubled mortgage company.
Gingrich said he was braced for more criticism from his remaining opponents and their allies. On Sunday, some Republican leaders voiced worry about Gingrich's combative style.
He also seemed to be enjoying the attention.
"I think you're going to see the establishment go crazy in the next week or two," Gingrich said.