Statistical models derived from the poll suggest that Obama's support would be as much as 6 percentage points higher if there were no white racial prejudice.It may be impossible to quantify the effect prejudice will have on the election. Certain other factors could compensate for or even magnify feelings about race - Obama's age, how closely he resembles black stereotypes, rumors he's Muslim, McCain's age, etc.
To the extent the Obama campaign can make the election one of issues rather than one of affinity, the chance that race becomes a decisive factor in the voting booth diminishes. And so McCain's choice of Sarah Palin, an affinity candidate, becomes all the more important to the Republican side.
It's in that regard that the Palin pick could pay off for McCain among Hillary Clinton supporters. It's not that she's a woman, it's that she's an attractive choice to those looking for a reason not to vote for Obama (despite their general agreement with him on the issues).
From the poll:
Among white Democrats, Clinton supporters were nearly twice as likely as Obama backers to say at least one negative adjective described blacks well, a finding that suggests many of her supporters in the primaries — particularly whites with high school education or less — were motivated in part by racial attitudes.*Update: Nate Silver at FiveThirtyEight.com has some interesting observations about the poll results and the so-called Bradley Effect (see comments).