For the record I think the direct political effects will be fairly minimal. In the states where it matters at all, I suspect any loss of support among culturally conservative Democrats and independents will be offset by a bump in youth turnout, which is a critical part of the Obama coalition. The recent college graduates living in their parents’ basement could use some concrete reasons to feel good about the guy they helped elect. It probably also helps draw a contrast with Romney, who promises to combine the exciting social norms of the 1950s with the bracing inequality of the 1920s. (Romney’s immediate reaction was to call Obama a “flip-flopper,” which is just adorable).
I don’t think Obama necessarily took the position primarily to score political points, but I believe (and hope) that he concluded it would not deal any fatal blows to his re-election. A politician who makes major decisions without weighing the potential loss of support has no business being president. It would have been a great thing for FDR to run for office on a platform of immediate federal desegregation, but I doubt it would have changed world history for the better.