American blacks tend to be (mainly; averaging 83%) Bantu, whereas Barack Obama is (half) Nilote.
http://www.google.com/search?q=site%3Aisteve.blogspot.com+ni...
http://isteve.blogspot.com/2008/01/east-africas-tall-vs-aver...
The tall black Nilotics generally see themselves as more intelligent than the shorter brown Bantus. Obama's Luo relatives in Kenya told him: "The Luo are intelligent but lazy." The Bantus tend to fear that they will be outsmarted by the Nilotics if they give them a fair shake, so they often treat the tall people like the Jews tend to be treated in Eastern Europe.
The dividing lines between the Nilotics and Bantus are not sharp. There's been lots of interbreeding. (This is Africa, after all.) But, they still exist. The situation is rather like that in Latin American, where after five centuries of interbreeding, the economic elites are still pretty white-looking, and the indigenous masses occasionally organize under demagogues like Hugo Chavez to fight back.