CHARLESTON, S.C. - Mitt Romney suggested at today's GOP presidential debate for the first time that he would "probably" release his tax returns not only from 2011 but from previous years as well, but garnered boos from the crowd when he seemed to waver on the decision.

Romney's announcement came the same night that rival Newt Gingrich released his tax returns for 2010, showing he made $3.1 million, and paid 31 percent of his income on federal taxes. Romney has said he paid about a 15 percent tax rate. That is the rate for capital gains on investments.

"When my taxes are complete for this year, and I know that if I'm the nominee, the president is going to want to insist that I show what my income was this last year, so when they're completed this year in April, I will release my returns in April for his year, and probably for other years as well," Romney said during the debate in Charleston, S.C., sponsored by CNN.

But when pressed whether he'd follow the path of his father, George Romney, who released 12 years of taxes during his 1967 presidential bid, arguing that there might be a "fluke" in just one year's results, Romney responded, "Maybe."

"I don't know how many years I'll release," Romney said as the crowd booed. Romney paused and smiled.

"I'll release multiple years, I don't know how many years," Romney said. "But I'll be happy to do that. I know there are some who are anxious to see if they can make it difficult for a campaign to be successful. I know the Democrats want to go after my being successful. I'm not going to apologize for being successful."

Financial disclosures with the Office of Government Ethics show Romney's net worth to be between $190 million and $250 million. Romney has used his business success and the focus of his career, not Washington politics but in corporate America and Massachusetts government, as a lynchpin of his candidacy, while at the same time trying to appear relatable to voters.

After Gingrich and Rick Santorum sparred about their records in Congress, Romney pointed to his experience as better suited to what America needs.

"What you've listened to, in my view, and the speaker's rendition of history going back to 1978 and his involvement in Washington, is, in my view, a perfect example of why we need to send to Washington someone who has not lived in Washington, but someone who's lived in the real streets of America, working in the private sector, who's led a business, who started a business, who helped lead the Olympics, who helped lead a state," Romney said, touting his own resume. "We need to have someone outside Washington go to Washington."

But that comment from Romney that he comes from the "real streets of America" drew an immediate response from Democrats, who, anticipating that Romney will ultimately be the Republican nominee, have tried to paint him more as corporate raider than successful businessman.

Romney had said two days ago that he would release only his 2011 returns.

"In prior races for president the tradition has been that the nominee releases his tax returns in tax season, in April," Romney said. "And I know that if I'm the nominee, people will want to see the most recent year, and see what happened in the most recent year and what things are up to date and so they'll want to see the tax returns that come out in April, so rather than sort of have multiple releases of tax returns, why, we'll wait until the tax returns for the most recent year are completed, then release them."

During the debate tonight, Gingrich suggested that if Romney had nothing to hide, he wouldn't wait to release his returns.

"He has to decide, if there's nothing in there, why not release them, and if there is something in them, better to know now," Gingrich said.

Former Sen. Rick Santorum said he didn't think Romney's returns are a "big deal."

Romney went on to justify his delay in releasing his returns by suggested that it would give Democrats fodder for attack.

"Because I want to make sure that I beat President Obama," Romney said. "And when we release things drip by drip, the Democrats attack. I pay my full taxes, I'm honest with people, I pay a lot of taxes, I've been very successful, and when I have my taxes ready for this year, I'll release them.