New York, Sep 30 : A month after Sarah Palin joined John McCain’s ticket to a burst of excitement and anticipation among Republicans, she heads into a critical debate facing challenges from conservatives about her credentials, signs that her popularity is slipping and evidence that her party is worried about how much help she will be for McCain.

Palin, the Republican vice-presidential nominee, flew to McCain’s ranch in Sedona, Ariz., on Monday for three days of preparation with a team of his aides — a sharp contrast to the less structured preparation that led up to the senator’s first debate, the New York Times reported.

The amount of time and staff power being devoted to this was evidence of concern among McCain’s associates that Palin’s early triumphs — a well-received convention speech, her drawing of big crowds — has been overtaken by a series of setbacks, creating higher stakes for her in the debate on Thursday with the Democratic rival, Senator Joseph R. 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,” David Frum, a former speechwriter for President Bush who is now a conservative columnist, said. “If she doesn’t perform well, then people see it.

Palin continues to draw large crowds is helping. McCain with fund-raising and drawing volunteers, and is drumming up support among base Republican voters who were once skeptical of his candidacy, party leaders said in interviews, the paper 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.

Her halting interview with Katie Couric on CBS News alarmed many Republicans and gave fodder for a devastating parody on Saturday Night Live, the NYT reported.

“I think the Katie Couric interview shows that she needs to be briefed more on certain aspects,” said Jim Greer, the Republican chairman in Florida.

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.

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