Help him? or hurt him?

A month after joining Sen. John McCain's ticket to a burst of excitement and anticipation among Republicans, Gov. Sarah Palin is heading into a critical debate facing challenges from conservatives about her credentials, signs that her popularity is slipping and evidence that Republicans are worried about how much help she will be for McCain in November.

Palin, the GOP vice presidential nominee, flew to McCain's home in Sedona, Ariz., on Monday for three days of preparation with a team of aides, a sharp contrast to the less structured preparation that led up to the senator's first debate.

The amount of time and staff power being devoted to this suggested concern among McCain's associates that Palin's early triumphs -- a well-received convention speech and subsequently attracting crowds at appearances -- had been overtaken by a series of setbacks, creating higher stakes for her in the upcoming debate on Thursday with the Democratic nominee for vice president, Sen. Joseph Biden.

"I think she has pretty thoroughly -- and probably irretrievably -- proven that she is not up to the job of being president of the United States," said David Frum, a former speechwriter for President Bush who is now a conservative columnist. "If she doesn't perform well, then people see it. And this is a moment of real high anxiety, a little bit like 9/11, when people look to Washington for comfort and leadership and want to know that people in charge know what they are doing."

Palin, of Alaska, continues to draw large crowds, is helping McCain with fundraising and drawing volunteers, and is drumming up support among base Republican voters who were once skeptical of McCain's candidacy, party leaders said. Yet these rough two weeks have led some Republicans to reconsider their initial assessment that she would sharply increase McCain's appeal among women and independent voters.

Interview alarming

Palin's interview with Katie Couric on CBS News alarmed many Republicans and gave fodder for a devastating parody on "Saturday Night Live."

Polling suggests that the number of Americans who think she is not fit to be president has increased since her introduction to the country last month. A number of conservative columnists and thinkers have publicly turned against her or criticized McCain for choosing her, including George Will, David Brooks and Kathleen Parker, who wrote a column entitled "She's Out of Her League" for the National Review Online.

The McCain campaign appears to be leaving nothing to chance. Palin will spend the next three days in debate preparation. She is practicing for the debate with Steve Beigun, a former staff member of President Bush's National Security Council; Randy Scheunemann, McCain's chief foreign policy aide; Mark Wallace, a deputy campaign manager for Bush's 2004 reelection campaign; and Nicolle Wallace, McCain's aide who was a communications director in the Bush White House.

"This debate will probably determine her political persona for the rest of the campaign," said Saul Anuzis, the Republican chairman of Michigan, another swing state where recent polling suggests that McCain is trailing.

Katon Dawson, the Republican chairman of South Carolina, said that the debate was important to clear up what he described as misapprehensions about her created by "a pile-on by the media elite."

"You don't have this kind of negative, media attack without a question mark being put up," she said. "She's going to have a chance to erase that question mark."

But Mike Murphy, who used to work as a senior adviser to McCain, said Palin's performance in the campaign had underlined his argument that Palin was a bad choice. Murphy said he was skeptical that she could turn it around in one debate. "She has the opportunity to undo some of the damage with a very strong debate performance," he said.

The rapid change in fortunes has led some Republicans to question the decision by McCain's advisers to restrict her exposure to unscripted settings -- town-hall-style meetings, news conferences or interviews -- saying such events would have helped prepare her for such high-profile interviews as the one she did with Couric.

"I disagree with the campaign's approach," said Rick Wilson, a Republican consultant. "I think they ought to toss her into the deep end from the outset."

Advisers said Palin was a diligent, hard worker and was frequently up until the small hours of the morning in her hotel room trying to cram as much as possible before the debate.