I'm looking at the electoral map here. I strongly believe that Senator McCain is enjoying his peak support right now. In other words, he doesn't have anywhere to go but down. The generic Democrat vs. Republican polls show a national lead for the Democratic nominee by as much as 15-20 points.
So when you see this map, look at the pink states and the pink-bordered states. These are states (Texas, Indiana, South Carolina, Florida, Nebraska, Ohio, etc) where Senator Obama can overtake Senator McCain between now and November.