"I understand the economy because I've lived in it," he said. "And by the way, I've been successful, but I've also lost. There's sometimes I failed. I probably learned more from failures than from the successes. But I know how this economy works."
Romney's relative silence was made possible, in part, by a gaffe by Newark, N.J., Mayor Cory Booker, an Obama supporter who on Sunday said exchanges by the campaigns over Bain were "nauseating" and a distraction from issues that interest voters. He walked back his comments after they dominated the campaign news for a day.
Obama is running television ads across five swing states featuring a former worker who likens Bain Capital to a vampire. The president's re-election campaign has also released Web videos and arranged multiple conference calls for reporters with employees from companies that suffered under Bain's leadership.
Romney senior aide Stuart Stevens described the television ad as "performance art gibberish."
"Shouting louder and getting more angry is not very persuasive," Stevens said in response to the line of attack. "The idea that people are walking around with less of a paycheck or higher gas prices because of something Bain Capital did 20 years ago is absurd."
Romney faced similar criticism from former House Speaker Newt Gingrich during the Republican primary. Gingrich accused Romney of "looting a company" and suggested that he return money earned "from bankrupting companies and laying off employees over his years at Bain."
The argument helped fuel Gingrich's surprise victory in South Carolina. Democrats are betting big that it will help Obama win over working-class voters in November, citing polling that suggests Romney would struggle with lower-income voters. But exit polling from the GOP primaries shows Romney won such voters about half the time.
In a rare interview on Bain, Romney told a conservative radio host last week that the closure of a Florida factory under Bain's control was not his problem. "The steel factory closed down two years after I left Bain Capital. I was no longer there. So that's hardly something which is on my watch," he said.
The Obama campaign has pointed out, however, that Romney continued to profit from Bain's investments years after he left.
Romney also opened himself to new criticism by resurrecting a controversy over the number of jobs he created at Bain. In the radio interview, he jabbed the Obama campaign for failing to mention that Bain created "over 100,000 jobs." He has struggled for months to back up the jobs claim.
The former Massachusetts governor co-founded Bain in the early 1980s, but left in 1999 to run the Salt Lake City Winter Olympics and pursue a political career. He has lived off his investments and retirement package ever since.
His net worth is now as much as $250 million, which would make him among the wealthiest presidents ever elected.
AP Deputy Director of Polling Jennifer Agiesta contributed to this report.
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