The map below tells it all. In the past two weeks Obama has surged (remember that word? It used to be a Republican word just weeks ago!) into the lead, right behind the largest calamity to befall the American economy in eight decades.
One way of predicting the outcome of a presidential election is to take the following formula: EB = NAR + (5*GDP)-25. That is, you can predict the winner (EB, electoral barometer) by taking the net National Approval Rating of the President (NAR) and add to it five times the growth rate of the economy (5*GDP) in the second quarter, and, if the party in power has occupied the White House 8 years or more, you subtract 25. The Gallup poll shows President Bush in early October to have a 25% approval rating, one of the lowest ever recorded for a president. The net, then, is -50 (75% disapprove). The economy in the second quarter grew at 3.3%, so five times this is 16.5. So up to here we are -50 + 16.5= -33.5. Subtract 25 from this, since Bush has been president 8 years and you get a whopping -58.5. This is the worst showing for an incumbent in more than half a century.