Repeat after me...there is ZERO chance of Pennsylvania going to Romney. Zero. None. Nada. Will not happen. Same with Michigan (I basically feel the same way with Wisconsin and Nevada...but I won't actually say that).
Put it this way, if either Penn or Michigan go to Romney, then he crushes in this election (and that's not going to happen).
This comes down to Ohio, Virginia, Colorado, Iowa, and New Hampshire. (maybe Florida, but I'm assuming that Florida will go to Romney...which certainly is not a gurantee).
If Obama wins Ohio...it's over.
If he loses Ohio, he needs Virginia and another.
If he loses Ohio and Virginia, he needs Colorado, Iowa and New Hampshire.
If Florida goes to Obama, he wins by a lot. If either Pennsylvania or Michigan go to Romney, he wins by a lot. In terms of the latter, read the first thing I just wrote. WILL NOT HAPPEN!