There are related trends in favorability; favorable views of Palin have dropped, for instance, by 20 points among white Catholics (from 69 to 49 percent), by 15 points among Midwesterners (who gave her a particularly favorable initial reception) and by 18 points among non-evangelical white Protestants.
There is strong partisanship in these views.
Sixty-seven percent of Republicans say Palin's experienced enough, compared with barely over one in 10 Democrats, and, as noted, a third of independents.
Eighty-four percent of Republicans view her favorably, and 75 percent think she understands complex issues. Conservatives and white evangelicals, both core Republican groups, also remain by her side.
The public's sense of Palin's grasp of the issues also is marked by partisan and ideological gaps. But among white women, a natural affinity group for Palin, barely over half, 52 percent, think she understands complex issues.
Naturally there's also partisanship in Biden's favorability rating.
But in terms of experience and grasp of the issues he holds majorities across the board; even among Republicans, 55 percent say he's experienced enough, and 66 percent think he grasps complex issues.
Results like these set up low expectations for Palin; it's possible she could advance simply by exceeding them.
But another possible dynamic was expressed by McCain himself last spring, when he noted that his age -- 72 -- increased the importance of his vice-presidential pick.
METHODOLOGY: This ABC News/Washington Post poll was conducted by telephone Sept. 27-29, 2008, among a random sample of 1,271 adults, including an oversample of African Americans (weighted to their correct share of the national population), for a total of 165 black respondents. Results among the 1,070 registered voters surveyed have a 3-point error margin. Sampling, data collection and tabulation by TNS of Horsham, PA.