I’ve been going over Electoral Vote scenarios for a side project (about to be released soon), gaming out the different plausible scenarios. Something surprising happened, I found that Obama can lose Florida, Ohio and Pennsylvania. All he needs to do is win Virginia and North Carolina (where he has been consistently up) and take either Nevada, Missouri, or Indiana. If he loses North Carolina he needs to win all three. Or he can just win Pennsylvania where he has enjoyed double-digit leads.
As I was writing this, Nate Silver of 538 posted Pennsylvanua Sanity Check making the same case, but with math:

Suppose that Barack Obama were to concede Pennsylvania’s electoral votes. Literally, concede them. Throw ’em back, like a Chase Utley home run at a Cubs game. How often would he still win the election?
…89.0% of the time, according to our most recent run of simulations, along with another 2.4% of outcomes that ended in ties. This is because in the vast majority of our simulations, Obama either:
a) was winning at least 291 electoral votes, meaning that he could drop Pennsylvania’s 21 and still be over 270, and/or
b) was winning at least 270 electoral votes, while already being projected to lose Pennsylvania in the first place.
(a) was much, much more common than (b), obviously.

Developing…