It might work that way for individuals - but I'd have thought it'd be balanced out (at least) by other people embarrassed to admit they were voting for Obama, because of social pressures. (I can't see where "union pressures" come into it with polls that aren't carried out by unions.)

But I can't agree with Ebbie - if people are worried lest they are falsely seen as racist, and over-compensate as a result, this is a reflection of the fact they live in a society where racism is a factor, but it isn't itself an expression of racism.