Political parties, especially of the R persuasion, are always looking for wedge issues, to drive a wedge between an opponent and voters. It seems to me that right now Dems are presented with a target rich environment of wedge opportunities, and the Mittster will get a wedgie in the process. Here's how it's going to work.
Dems in congress will (or should) keep bringing up legislation aimed to help the middle class, or women or minorities, or young people. Because Rs refuse to go along with almost everything, they will oppose this stuff, or want to. Like the student loan interest rate reduction. The Mittster, on the other hand, needs to move to the center, away from the crazy edge of R politics where he's spent the last few months.
So, Mitt will tend to separate from the Rs (thereby making Obama look that much more reasonable). Or, he'll hang tough on the right and alienate those core constituencies, which will help Obama.
So there's the choice. Mitt can try to broaden his appeal, and in the meantime make Rs look bad and Obama look good, or he can cleave to the right and hurt his chances of getting elected. Beauty. And BTW, some decent legislation might end up getting passed, like the Violence Against Women Act.