Given that Mondale and Reagan were quite close over the summer, I find it quite possible.
The president's opponents feel so strongly about him that there's no way any of the McCain states (namely Missouri and Arizona) will vote for him this time.
"Gov. Walker's opponents feel so strongly about him that there's no way any of the Barrett counties will vote for him this time."
...
In 2004, GWB's opponents felt VERY strongly about him, and he still managed to pull it out, and even to increase his PV percentage by about 3 points over 2000. I'm not saying that's likely to happen with Obama (it isn't), but just because Republicans are motivated, it doesn't mean it's enough to defeat an incumbent president.
You're right, but since this election will probably be closer than 2008, I don't see it happening. 2000 was one of the closest presidential elections in history, after all, and GW Bush carried all of the Dole states from '96 and then some. I think you will see something similar with Romney this time, regardless of who wins the election.