SCENARIOS - How the Palin-Biden debate could play out

Television crew look at the stage for the first 2008 U.S. vice presidential campaign debate in St. Louis, Missouri October 1, 2008.

REUTERS - The showdown on Thursday between Republican Sarah Palin and Democrat Joe Biden is the only vice presidential debate of the White House race, and it has attracted more attention than usual because of high interest in Palin.

Palin, the governor of Alaska, was a virtual unknown when John McCain tapped her to be his No. 2 in August. But the mother of five quickly became a celebrity and rallied enthusiasm among conservatives.

Biden, the Senate Foreign Relations Committee chairman and one of the party's most experienced foreign policy hands, was picked by Barack Obama as his running mate to ease concerns about Obama's relative lack of experience.

Some of the potential scenarios for their debate at Washington University in St. Louis, Missouri:

-- Palin, 44, has been shielded from reporters, giving only three interviews since being named McCain's No. 2, and she appeared hesitant and heavily coached in those sessions. She does not need to be a policy expert, but must prove herself capable of stepping into the presidency if anything happens to McCain. At 72, he would be the oldest president to start a first term.

-- Biden, 65, has a reputation for being verbose, mistake-prone and at times condescending. If he is aggressive with Palin it could backfire, so he is most likely to talk directly to the audience about Obama and McCain and largely ignore Palin.

-- The candidates will stand at podiums and foreign and domestic policy will be covered. But a discussion of congressional action on a bailout of the U.S. financial industry is certain to dominate.

-- Vice presidential debates are usually ho-hum affairs, but the audience for this nationally televised encounter could surpass the 52 million who watched the first debate between Obama and McCain last week. It could become the most watched vice presidential debate ever.

-- The previous record was the nearly 57 million who watched the 1984 debate between then-Vice President George H.W. Bush, the current president's father, and Geraldine Ferraro, the first woman vice presidential nominee for a major party.