The Black columnist in the NY Times has been grousing about Obama for some time.
Good observation. Why do you suppose that is so?
Is the black population sufficiently large in those respective states to have made a difference in the election results?
Motivated, organized people vote in midterm and special elections.
Let me be more specific: self-motivated, self-organized people vote in midterm and special elections. These are NOT the sort of people who can't get off their duff long enough to be legally registered to vote and get to the polls under their own steam.
The 2008 election of BO was in large part about novelty: BO, the first "black" President.