Looks like he may be losing both conservative Democrats and some independents...
From Gallup polls:
...support for Obama among all Democratic registered voters fell from 81% in early August (Aug. 4-10) to 78% last week (Aug. 18-24). Obama's support from Republicans over this period also dipped from 9% to 7%, while 42% to 43% of independents have consistently supported him.
Now I realize that polls are little more than snapshot of current public opinion but this particular one happens to mirror some of the talk I'm hearing amongst moderates both online and off. I can't help but think that part of this loss of support from the middle has to do with the fact that many moderates were waiting for Obama to unveil innovative and thoughtful policies. However as the race has moved to the middle and the distinctions between Obama's economic and energy policies and McCain's become less clear the more that works in McCain's favor. He is after all a figure that the political center of this country knows pretty well. Obama? Not so much.
If Obama doesn't start defining exactly what change is going to look like many independents and moderates may decide to back the devil they know over the devil they don't.