(CNN) -- Newt Gingrich on Friday called on rival Republican presidential candidate Mitt Romney to release records to back up the Republican front-runner's claim last month that he helped create 100,000 jobs at Bain Capital, the private equity firm that has become a central issue in the campaign of late.
"You can't run for president, have half your campaign be about your great achievements and then hide them, and it is silly to try," Gingrich said in remarks to a crowd of Cuban-Americans at the Cafe Versailles coffee house in Miami.
"If he can't stand up today and defend his claim today, how is he going to stand up to Obama in the fall?" he said.
As it happens, Romney didn't need to wait until fall, as President Obama's campaign fired off an e-mail blast to supporters on Friday calling Romney a "corporate raider" for his role at Bain.
Romney's work at the private equity firm has become a target of Gingrich and fellow GOP candidate Rick Perry, who have accused Romney of adding to his wealth by cutting jobs at companies in which Bain invested.
At the Miami stop, Gingrich said Romney himself appeared to be changing the claim in a new ad, which states the candidate and Bain together created "thousands" of jobs, not the 100,000 he touted as recently as Thursday.
Speaking at a campaign stop in South Carolina on Friday, Romney defended his record.
"A lot of people want to talk about how we create jobs," Romney said. "By the way -- it is not to walk away from free enterprise. It is not to say that there is something wrong with the free market system. No, it is to hold fast to that system and to make it work for the American people."
Romney's campaign also released a television ad in South Carolina challenging the attacks.
"We expected the Obama administration to put free markets on trial," the Romney ad said. "But as the Wall Street Journal said, Mr. Romney's GOP opponents are embarrassing themselves by taking the Obama line."
Gingrich said Friday he would ask supporters at a political action committee to edit or pull an advertisement depicting Romney's role at Bain as a mission to "reap massive rewards for himself and his investors" by gutting companies and killing jobs.
The ad, called "King of Bain," earned a "four Pinocchio" rating on Friday from the Washington Post, which said "it is a stretch to portray Romney as some sort of corporate raider."
But he said Romney has issues of his own in his new ad. The former speaker pointed to a recent Washington Post fact-checking column that gave the 100,000 jobs claim "three Pinocchios."
In a news release issued Friday, Gingrich said the claim was "as inaccurate as President Obama's claim to have 'saved or created' millions of jobs."
"Furthermore, Gov. Romney's experience as a portfolio manager did not help him create an environment in Massachusetts that was friendly to job creation," Gingrich said in the statement. "As Gov. Mitt Romney raised $700 million in taxes and fees, despite a campaign pledge not to, and Massachusetts ranked fourth worst in job creation under his leadership."
South Carolina voters go to the polls on January 21 in the next GOP primary in the contest to select a candidate to face Obama in November.
A new American Research Group poll released Friday finds Romney and Gingrich in a statistical dead heat in the state.
According to the poll, 29% of likely GOP primary voters say they will support Romney. Another 25% said they would support Gingrich, putting Romney's lead within the poll's sampling error.
The survey indicates Rep. Ron Paul of Texas has 20% of the vote, Texas Gov. Rick Perry has 9%, former Sen. Rick Santorum of Pennsylvania has 7%, and Jon Huntsman, the former Utah governor and U.S. ambassador to China, has 1%, with 7% undecided.
CNN's Rachel Streitfeld, Jessica Yellin, Jim Acosta and Alan Silverleib contributed to this report.