One chart tells the tale.
http://politicalticker.blogs.cnn.com/2012/11/07/mcdonnell-they-beat-us-on-the-ground/
it seems Obama manged to win because he ran the most negative campaign in history, outspending Romney and portraying him as a guy that doesn't care.
The Dems had a better ground game. The Romney people admitted it themselves.
http://politicalticker.blogs.cnn.com/2012/11/07/mcdonnell-they-beat-us-on-the-ground/