Well, perhaps you CAN take the Africa out of Africa, but in the case of Obama it's a case of his putting on a black accent because he's playing Demagogue and Rabble-Rouser that particular day. You wil notice that the rhythms and inflections of his speech shift from audience to audience, so that one day he's addressing "the people" and the next he's in front of "the folks." Like most gifted charlatans, he knows how to work a crowd, and the fact that so many of them are fatuous enough to get the vapors every time he opens his mouth just makes his work that much easier. One could make the case that working the crowd is the closest he has ever come to actually doing a job. Still. his act is strictly for the rubes.