The division lines aren't that clear. Here's the 2008 election map by county, with shades of purple instead of red/blue:
http://www-personal.umich.edu/~mejn/election/2008/countymappurpler1024.png
Now try drawing a clear cut line on that map....
Here's the 2004 map, which is very similar:
http://www.princeton.edu/~rvdb/JAVA/election2004/purple_america_2004.gif
For more stuff like that (including the wacky population distorted maps), check out
http://www-personal.umich.edu/~mejn/election/2008/. We're not as divided as some would like to think.