Nate Silver explains (in characteristically excellent fashion) why there are so few black senators and governors:
I suspect that a lot of the problem, however, is that as Congressional Districts have become more and more gerrymandered, leading to the creation of more and more majority-minority districts following the 1980 and 1990 censuses, the black political apparatus has become more and more ‘ghettoized’. Black candidates have not had to develop a message that appeals to white voters, because most of them don’t have very many white voters in their districts (about half the nation’s African-American population is limited to the 60 blackest Congressional Districts). Nor do they have very many conservative voters in their districts, and so they have not had to develop a message that appeals to conservatives, even though the black population itself is far more diverse in its political views than is generally acknowledged.
Because they are not very representative of their states as a whole, moreover, these districts are also not likely to be very good launching pads for ascension to the Senate or to the governor’s mansion. Do I think Jesse Jackson Jr. would have some trouble winning statewide office? I do — but I also think that Pete Stark, who lives in a mostly white and Asian but extremely liberal district in the Bay Area, would have trouble becoming a senator in California.
This analysis implies that we’ll see more high-ranking black elected officials only as more aspiring black politicians cut their teeth in relatively culturally/politically diverse areas. Incidently, this generation of African-Americans (at least, those on the higher end of the income scale) are far more likely than their parents to live in areas which aren’t dominated by African-Americans. As more and more African-Americans attend mixed high schools and graduate from predominantly white academic institutions, I’m fairly certain that we’ll see more African-American politicians aiming higher than a House seat.