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.