Ahead of Thursday debate, McCain running mate’s popularity begins to slip

A month after Gov. Sarah Palin joined Senator 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 Republicans are worried about how much help she will be for Mr. McCain in November.

Ms. Palin, the Republican vice-presidential nominee, flew to Mr. 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 amount of time and staff power being devoted to this was evidence of concern among Mr. McCain’s associates that Ms. 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 Thursday with the Democratic nominee for vice president, Senator Joseph R. Biden Jr. of Delaware.

“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 in an interview.