Tampa, Florida (CNN) - Mitt Romney offered a stark warning to fellow Republicans that nominating Newt Gingrich could end in a series of surprises that could torpedo the party's hopes to re-take the White House in the fall.
Calling the former House speaker "highly erratic," Romney cautioned they could see "an October surprise a day from Newt Gingrich," if he were to become the GOP nominee.
Follow the Ticker on Twitter: @politicalticker
"He's gone from pillar to post almost like a pinball machine, from item to item in a way which is highly erratic and does not suggest a stable, thoughtful course which is normally associated with leadership," he told reporters in Tampa Monday.
The harsh rhetoric is the latest escalation in a wildly shifting race between the two men that has become increasingly negative as the party girds for a drawn-out nomination fight.
Days after Romney said in a CNN debate that he regretted the time he spent discussing his opponents instead of President Barack Obama, the candidate changed course after a resounding defeat by Gingrich in South Carolina.
Speaking with reporters, he called on Gingrich to release a list of detailed documentation: the "work product" from his work with troubled mortgage giant Freddie Mac, records from a House ethics investigation into Gingrich's activities as speaker, and a client list from Gingrich's post-congressional career – activity Romney labeled "lobbying."
"At the time he was lobbying Republican congressmen for Medicare Part D, was he working, or were his entities working with any health care companies that could have benefited from that?" Romney said. "That could represent not just evidence of lobbying but potentially wrongful activity of some kind."
Romney also called on Gingrich to return the seven-figure sum his firm earned for its work with Freddie Mac.
Gingrich has said the majority of that sum went to pay overhead and for staff at his firm.
Romney's press conference followed a housing roundtable in which Romney laid the groundwork to tie Gingrich to the foreclosure crisis gripping Florida.
The GOP candidate listened sympathetically to a group of Floridians who had suffered from falling home values and a troubled mortgage market. One woman said she could not find work and said her home was in the foreclosure process, while another man said he had considered moving out of the country in an effort to make his funds stretch further.
Romney blamed a list of agencies for failing to predict and prevent the growing housing bubble.
"There was every effort on the part of the banking industry, Wall Street, Congress, the banking guarantors Freddie Mac and Fannie Mae to keep it going," he told the group.
Later he made the connection to Gingrich more explicit.
"I wish Speaker Gingrich was here this morning to listen to those stories," Romney told the media, saying he hoped Gingrich had told Freddie Mac: "that this was a crisis about to erupt and it could be devastating to the economy to American families and that there should be a dramatic shift in the policies of Freddie Mac as well policies of government."
He added: "I didn't hear that nationally I didn't hear him making those warnings to the nation."
Meanwhile, the Romney campaign also released a harsh new television ad attacking Gingrich for having "cashed in" on the foreclosure crisis.
"While Florida families lost everything in the housing crisis, Newt Gingrich cashed in," the ad said.
The former Massachusetts governor defended his new attacks on Gingrich Monday as a description of "distinctions" between himself and the other GOP hopefuls, and signaled he would continue this new tack in two debates this week in Florida.