On the money, I'd say:
Clinton won Pennsylvania for two key reasons: Only Democrats could vote in the primary, and the Keystone State electorate is dominated by the elderly, who are staunchly for Clinton. Despite her claims of electability, Hillary has never done well among independent voters. And Obama usually loses the Democrats. Pennsylvania's closed-primary rules gave her a key advantage.
Older voters are flocking to Clinton as fears mount of what Obama might do as president. But those under 45 - less focused, perhaps, on race - are moving toward Obama. Here, that split helped her.
Does anyone believe that the big difference in voting patterns between the young and the old have nothing to do with residual racial attitudes?
2006-2011 archives for The Daily Dish, featuring Andrew Sullivan