With her campaign on the line, Clinton has aggressively challenged Obama in the last few days, questioning his readiness to become commander in chief and chiding him for the health care campaign literature sent to Ohio voters.
In the debate, she attacked Obama for claiming she supported the North American Free Trade Agreement, which she said she believes should be renegotiated. She was first lady when her husband, President Bill Clinton, approved the deal.
The trade agreement is unpopular in Ohio, where it has been blamed for contributing to a broad loss of manufacturing jobs in the state.
"You know, I have been a critic of NAFTA from the very beginning. I didn't have a public position on it because I was part of the administration. But when I started running for the Senate, I have been a critic," Clinton said.
Obama repeated the charge and said he would push to have NAFTA redone.
"I think that it is inaccurate for Senator Clinton to say that she's always opposed NAFTA. In her campaign for Senate, she said that NAFTA, on balance, had been good for New York and good for America," he said.
Clinton complained about having to take the first question more often than Obama, and made reference to her campaign's charges that he gets an easier ride from the national media than she does.
She pointed to a television skit that portrayed a fawning press posing questions to Obama.
"If anybody saw 'Saturday Night Live,' you know, maybe we should ask Barack if he's comfortable and needs another pillow," she said. "I just find it kind of curious that I keep getting the first question on all of these issues."
Clinton, who has questioned Obama's foreign policy experience, also stumbled over the likely new Russian president when asked if she knew the name of the successor to President Vladimir Putin - Dmitry Medvedev.
"Medvedev - whatever," she finally said.
The two contenders revisited their differences on the Iraq war. Clinton said Obama, an early opponent of the war, had the advantage of not being in the Senate in 2002 when she voted to authorize the war.
But Obama said her vote "facilitated and enabled" President George W. Bush's decision to go to war.
"Senator Clinton often says that she is ready on day one, but in fact she was ready to give into George Bush on this critical issue," Obama said.
