I think he should run for Congress against Rush or Davis. If he got 30% of the city black vote but 80% of the suburbs (a simply majority in each town), he'd win. Both Davis and Rush are waaaaaaay too liberal for their suburban electorate, and only have so many suburban consitutents so Illinois can squeeze in three black districts.
The U.S. Senate is a much harder prospect, although it is good to see more black conservatives moving here. A Fairman-Obama race WOULD be interesting though, except it's doubtful either would win his party's nomination.
Bush got about 16% in both those seats. Winning either of them is a pipe dream.
I think Obama has good chance to win the rat nod.