William Kristol writes in the NY Times in his column "The Shape of the Race to Come:"
More fundamental will be the question of the discrepancy between the image of Obama the uniter and the reality of Obama the liberal. That hasn’t been much of a problem for Obama in the Democratic contest, since Clinton hasn’t attacked from the right or even the center.
But Republicans will. Last week, over drinks, one Republican strategist not affiliated with the McCain campaign mused about how an independent advertising effort against Obama might work. “Barack Obama: He’s not who you think he is” would be the theme. The supporting evidence would come from his left-wing voting record in Illinois and Washington, spiced up with fun video clips of Reverend Wright.
The essential misjudgment that countless people have made about Obama is assuming that being half-white makes him more ideologically moderate. It's an easy assumption to make: if 88% of blacks voted Democratic in 2004 vs. only 41% of whites, then somebody who is half-black and half-white should fall in-between, right? It's simple arithmetic!
In reality, the opposite is true. Somebody who is as white as Obama in upbringing and personality, but as black by avocation and profession, has to constantly prove he's "black enough." Since Obama's a Primarily Political Person, as Michael Blowhard might say, he has to repeatedly prove he's black enough politically.
Obama's basic political psychology isn't at all complicated -- it doesn't take a high degree of empathy or psychological acuity to figure out the basic theme of Obama's life -- but it's remarkable how he got to the point of almost having the Democratic nomination for the White House wrapped up before the press starts to figure it out.