why didn't the bradley effect apply to obama?

i don't know.

one hypothesis is that, at least in the primary, clinton's own bradley effect (as a woman) was actually more powerful, and that the sexism overpowered the racism. that might actually be true, but you're stacking hypotheticals. who knows, really.

another thing to point out is that the nature of obama's coalition was hard to poll, in the first place. my memory of 2008 was that obama's vote was incredibly efficient, so you just might end up accidentally undoing a bradley effect by weighting the polls badly, in trying to peg his support, which was very intensely concentrated in urban regions.

a third suggestion is that he was just an enigma; every rule has exceptions.

but, i'm actually going to throw this out there: barack obama is actually white. well, it's true - he's white in almost every way. you have to bring in jim crow laws to decide he's black. i know a lot of people won't really like this analysis, but the fact is that he massively played up his kansas roots & his white mother, and while he can "pass as black" when he has to, he's more comfortable in an essentially culturally white exterior.

so, it could be that the bradley effect didn't apply to obama because voters didn't really interpret him as black.