Blago got in the way of Valerie Jarrett being given Obama's vacant seat.
https://en.wikipedia.org/wiki/Rod_Blagojevich_corruption_charges
Obama's involvement
Blagojevich was aware that Barack Obama would have preferred "Senate Candidate #1" (Valerie Jarrett), and he allegedly made efforts to obtain favors in exchange for appointing Jarrett for the U.S. Senate seat.[11] Blagojevich said in a conversation with his chief of staff, in reference to what Obama would give him in exchange for Jarrett's appointment, "All they're going to give me in return is gratitude. The Senate seat's a fing valuable thing. Fk them."