Mr. Frum noted the difficulty that Dan Quayle, who was elected vice president in 1988, had in recovering from an early set of mistakes that led him to be ridiculed as an intellectual lightweight. “The story of Dan Quayle is he did probably 1,000 smart things as vice president, but his image was locked in and it was very difficult to turn around,” he said. “And Dan Quayle never in his life has performed as badly as Sarah Palin in the last month.”

Several Republicans said that all of this could ultimately play to Ms. Palin’s benefit, lowering expectations for her so much that a mediocre performance in the debate could be hailed as a success.

“Thanks to the mainstream media, quite a low expectation has been created for her performance,” said Ron Carey, chairman of Minnesota’s Republican Party. “The style of Sarah Palin is going to amaze people. She is going to be able to amaze people with the substance she is going to deliver.”

And Mr. McCain’s aides disputed the expressions of concern and said that if anything, the barrage of criticism and the performance in the few television interviews she has done gave her a low bar to clear in the debate. “I seriously hope that people continue to underestimate the most popular governor in America and a woman who speaks to the heart of America’s economic angst,” said Nicolle Wallace, a senior adviser to Mr. McCain.

And Mr. McCain, appearing with Ms. Palin in another interview with Ms. Couric on Monday night, offered a hearty endorsement. “I’ve seen underestimation before,” he said. “I’m very proud of the excitement that Governor Palin has ignited with our party and around this country. It is a level of excitement and enthusiasm, frankly, that I haven’t seen before.”

Ms. Palin is getting ready for the debate at a time of enormous uncertainty about a highly complicated issue, the unfolding crisis on Wall Street, which makes preparing for the face off especially hard.

And the McCain campaign appears to be leaving nothing to chance. Ms. Palin will spend her preparation time at Mr. McCain’s vacation compound in Sedona, with her husband and children. She is practicing for the debate with Steve Beigun, a former staff member of Mr. Bush’s National Security Council; Randy Scheunemann, Mr. McCain’s chief foreign policy aide; Mark Wallace, a deputy campaign manager for Mr. Bush’s 2004 re-election campaign; and Ms. Wallace, who was a communications director in the Bush White House.