This officially has me concerned about Romney's appeal in the South. We need to see a poll of GA. If he's in a statistical tie or behind, that would negate his entire advantage over Huckabee, which is the West. I think Huckabee can be considered the strongest opponent for now. He would make PA and especially IA close enough that he could potentially eek out a win without CO and NV.
I actually think the Republicans can win without CO, NV or NM. As far as Huck is concerned, I think this is his path to election:
The light blue areas are places I think he can pick up from Obama 2008. (Huckabee would have lost in 2008, but with the 2010 census, he wins 272-266.)