i don't think obama said he was black. he's always said he was biracial. i think society groups him as black and black americans embrace and accept him.
perhaps the question should be asked why doesn't white america embrace him as one of them?
black americans are products of slavery and have lived in this country for hundreds of years. his black ancestry is directly from africa. culturally he shares very little with black americans.
he has been raised by his white family members and didn't even "get" black people as he was growing up.
it's kind of absurd how he's been painted as this black radical just because he has black features and a black wife.