WASHINGTON -- Documents filed by Mitt Romney's former company conflict with the Republican presidential candidate's statements about when he gave up control of the private equity firm Bain Capital. President Barack Obama's campaign seized on the discrepancies Thursday to charge that Romney was lying about his background.

Romney, in turn, said Obama was the one being dishonest, rolling out a hard-hitting television ad that accused the president of launching "misleading, unfair and untrue" attacks about the Republican's role in outsourcing U.S. jobs.

"When a president doesn't tell the truth, how can we trust him to lead?" the narrator says in the Romney ad titled "No Evidence."

Obama has accused Romney of being an "outsourcing pioneer" who invested in companies that shipped jobs to China, India and elsewhere overseas. But Romney, who has made his business experience the central part of his candidacy, claims he had no role in outsourcing U.S. jobs because much of that activity didn't happen until after 1999, when he says he had given up operational control at Bain.

Both candidates dug in on their positions, dispatching aides to level deeply personal criticisms aimed at casting each opponent as little more than a typical politician. Each candidate is seeking to sully his rival's integrity in hopes of gaining ground in closely contested campaign four months before Election Day. But the strategy carries risks: It could alienate voters — especially critical independents — who are turned off by negative campaigning and want to see the candidates focus on the economy and job growth.

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