Surviving 90 minutes on a stage with Biden did not transform Palin into a plausible president.

E.J. Dionne, Jr. writes in The Washington Post:

Early in last night's vice-presidential debate, Sarah Palin said that she might not answer the questions as moderator Gwen Ifill posed them. This was the Alaska governor's way of saying she was going to stick to the talking points she had stuffed into her head, no matter what the subject.

When Palin described John McCain's health-care plan, she talked about his offer of a $5,000 tax credit so families could buy insurance. She failed to mention that McCain would pay for the credit by taxing existing insurance benefits. Democratic vice-presidential nominee Joe Biden -- politely -- pounced on her omission, warning that McCain's plan could lead millions to lose their insurance coverage. Palin didn't come back to defend her running mate.

Nor did she come back when Biden challenged her false claims about how many times Barack Obama had voted for tax increases. Palin just plowed forward, piling one attack on top of another, with leavening references to "Joe Six-Pack" and "hockey moms."

Oh, yes, she did correct Biden on one thing. When he said the Republican energy slogan is "drill, drill, drill," she quickly reminded him that "the chant is drill, baby, drill." Thanks for clearing that up.

Last night's debate took place at the moment when a majority of American voters had decided that Palin was unprepared to be president if she were called upon to assume the office. Surveys by The Post and ABC News and by the Pew Research Center both found that doubts about Palin have risen sharply since the beginning of September.

The key to understanding how McCain chose Palin as his running mate was provided by the New York Times last weekend when it described an episode in which he "tossed $100 chips around a hot craps table." Americans are increasingly uneasy about the gamble they might take by putting Palin a heartbeat away from the presidency.

Expectations for Palin were so low that the mere fact that she managed to keep talking and to keep assailing Obama will be rated as a great victory by McCain's lieutenants. But it was Biden who knew what he was talking about, who could engage in argument and who showed he actually understood the issues. In recent interviews with CBS anchor Katie Couric, Palin came off as profoundly uninformed, as someone who had given little thought to the issues that will matter. Nothing Palin did last night changed that. Those rooting for her were relieved. Those who doubted her readiness going in were not persuaded by her endless repetition of the word "maverick."

Palin has also brought out the very worst in McCain, forcing him to -- and I do not use this word lightly -- lie about her. In an interview broadcast Wednesday, National Public Radio's Steve Inskeep asked McCain if there would be "an occasion where you could imagine turning to Governor Palin for advice in a foreign policy crisis?"

McCain replied: "I've turned to her advice many times in the past. I can't imagine turning to Senator Obama or Senator Biden, because they've been wrong."

" Many times in the past?" McCain met Palin only twice before he selected her. What McCain said could not be true. And would anyone who listened to her last night really consult Palin on foreign policy?

This week, McCain's backers signaled their fears that Palin would fail by trying to discredit the debate in advance. Although it has been known at least since July that Gwen Ifill was writing a book on "Politics and Race in the Age of Obama," the usual right-wing attack squad waited until two days before the debate to mount a campaign to the effect that Ifill's book project turned her into a biased moderator. In her measured questioning, Ifill showed that the attack was nonsense.

The core issue, of course, is the contrast between how Obama and McCain chose their running mates. Say what you will about Joe Biden -- and last night, he was far from being either the gaffe machine or the windbag so many predicted would appear on stage -- no one loses sleep at the idea of his being in the Oval Office. Obama picked a vice president more likely to help him govern the country than win the chance to do so.

As for McCain, he found himself in a political hole and threw the dice with Palin. At the time of her selection, voters were often compared with "American Idol" watchers who put personality and stage presence above everything else. But it turns out that Americans take the presidency very seriously. And surviving 90 minutes on a stage with Biden did not transform Palin into a plausible president.