Dan Quayle, who was George H. W. Bush's 1988 running mate, lost his debate against Lloyd Bentsen by a wide margin, according to polls at the time. But the event had no significant impact on the election, which Bush and Quayle won easily.
Four years earlier, Bush debated Geraldine Ferraro, the only woman on a major-party ticket until Palin, but drew more attention for a remark the next day. "We tried to kick a little ass last night," Bush told a New Jersey man in a comment picked up by a TV microphone and seen at the time as a blunder.
The former president's experience underscores the difficulty that Biden, or any male candidate, faces in debating a woman. He's been preparing by sparring with Michigan Gov. Jennifer Granholm in mock debates.
Democratic strategist Jenny Backus said it would be a mistake for Biden to go after Palin directly.
"He can't attack her just to attack her, just to score points," she said. "People are already assuming he's more qualified. Biden has to make the debate about McCain and make Palin answer for McCain's record."
McCain's age - 72 - and history of health problems, including the deadliest form of skin cancer, have the potential to make his running mate unusually important to undecided voters. Liberal groups have run graphic TV ads attacking McCain's health history in an indirect effort to exploit doubts about Palin.
Biden has his own vulnerabilities, including as a debater, though he got generally high marks for the way he handled himself in more than a dozen joint appearances in the '08 primaries.
His reputation for long-windedness produced a memorable debate moment last year. Biden was asked, at a South Carolina forum, about his reputation for "uncontrolled verbosity" and as a "gaffe machine" and whether he had the discipline for the world stage.
"Yes" was his one-word reply, which prompted knowing laughter from the audience.
Palin, a practiced TV presence from her days as a local sports anchor, has sought to lower expectations, and turn Biden's years of experience against him.
Palin said she was looking forward to meeting Biden, adding that she'd "been hearing about his Senate speeches since I was in, like, second grade."
McCain himself, in a clear reference to Biden, suggested that his longtime colleague had "spent too much time inside the [Washington] Beltway" instead of being "in touch with the American people."
Polls show that voters view both vice presidential candidates favorably on a personal level. However, unfavorable opinions of Palin have increased among independents, women and voters between 30 and 49 - her own age bracket, the Pew survey found.
The poll also showed that fewer than half of women voters said they considered Palin well-informed, with a sharp divergence between married and unmarried women. A majority of married women said she was well-informed, while unmarried women said she was not.
This week, McCain grew defensive when asked about voter concerns over Palin's level of experience and recent criticism of her from conservatives.
"If there's a Georgetown cocktail party person who, quote, calls himself a conservative who doesn't like her, good luck, good luck," McCain told the Des Moines Register. "I think the American people have overwhelmingly shown their approval."
