Nate Cohn expects this week's polls to be highly significant:
If Obama’s four point lead persists through the week, Obama should be considered a very strong favorite for reelection. While it might seem that the heart of the campaign is still to come, the candidate leading two weeks after the in-party convention has gone onto win the popular vote in every presidential election since Truman's come from behind victory in 1948. And the only other comebacks were also staged by candidates or incumbents who ascended to the presidency or the nomination following resignation, assassination, or a late decision not to seek reelection.
Here's the whole graph skewed by Rasmussen and with heightened sensitivity to outliers:
And here's a key state, Florida, and the latest state of play:
Nate Cohn continues:
Truman, Ford, and Humphrey gains are hard to analogize to other contests involving incumbents, given that the candidates were forging their own electoral coalitions for the first time out of the fragmented remnants of older ones. And although Romney is behind by just four points, the race has been unusually stable and Obama may be at or very near 49 percent of likely voters, which means Romney would need to win an extremely large share of an unusually small number of undecided voters to overcome a seemingly tiny deficit.
The Dish 