Take a look at the electoral map right now. I like the one produced over at Electoral-vote.com:
Solid red or blue means huge leads, 10 points or more. Light blue or red means big lead, between 5 and 9 points. White with a light red or blue border means "barely", 4 points or less. The percentages are based on the most recent poll or polls (with a week of each other) in each state.
On this map, President Obama would win every single state he did in 2008 except Indiana. The electoral tally would be: Obama 347, Romney 191.
There are only 6 states in the "barely" category right now, all blue: FL+4, IA+4, CO+3, VA+2, NH+2 and NC+2.
What if there was a sudden national shift toward Romney? I know, this is hard to imagine, but just play along. He is so impressive in the first debate (no really!), for example, that he closes 5% on Obama in every single swing state.
In this nightmare scenario Romney would flip all 6 of those close states. Ack! Final tally: Romney 267, Obama 271.
Obama would still win.