Did Obama indirectly secure a victory for Proposition 8

According to exit polls, African Americans in California voted 70% in favor of Proposition 8.

More on this and related Prop 8 issues:
Megan McArdle: The people have spoken
Andrew Sullivan: Oh, No, You Don't
Obsidian Wings: Prop 8 and the Black Vote
Coates: Work to do
LA Times: Gay-rights advocates to challenge Proposition 8 in court