Obama spokesperson Bill Burton argues, via instant messaging, that the exit polls show already that in Pennsylvania Obama is doing better among key groups than he did in Ohio, a state with similar demographic advantages for Hillary:

Significant improvements over Ohio, especially among white men and seniors overall.

With voters over 60 in OH, Clinton won 69%, Obama got 28%. In PA, Obama earned 41% of the vote among voters over 60, and Clinton won 59%. The gap among seniors was cut by more than half, from 41 to 19.

Among white men, in Ohio, Obama got 39%, in PA, 46%. Clinton was at 58% in OH and dropped to 53% in PA. The gap narrowed from 19% to 7%.

It's worth keeping in mind that for various reasons Pennsylvania is actually more demographically advantageous to Hillary than Ohio was -- a fact that could either redound to her benefit or to her disadvantage, depending on what happens tonight.