From Time magazine:
While recent national polls show Clinton matching up well against every potential Republican competitor, the picture looks very different in Republican and swing states. Says a purple-state Congressman who is nervous about holding onto his seat if Clinton is the nominee: "She certainly will get Republicans riled up. They will not only go out and vote against her--they'll stop off at their neighbors' house along the way and drag them to the polls."
A late-October Quinnipiac University survey underscored this point. Nationally, it showed Clinton being edged out by former New York City Mayor Rudy Giuliani, 45% to 43%, within the margin of error. In red states, however, she ran behind him, 49% to 40%, and she trailed, 47% to 41%, in the purple ones. By comparison, Illinois Senator Barack Obama beat Giuliani by a single percentage point (43% to 42%) nationally but held that same margin in the purple states and came within 6 points (45% to 39%) in the red ones.
So, in essence, Clinton runs up her margins on the coasts and lags everywhere else. Eeek. You could argue that Obama will decline in purple and red states as he gets better known; at the same time, he'll probably rise in blue states. Still, this is not a heartening picture...