the math (pre-debate baseline)
I'd expect that trend to continue. But the thing I'm still struck by is how stable the overall picture seems to be in post-conventions month. I don't expect the debates to move things much. And at this point, if you think there is enough volatility left in the system to swing the election to Mr. Romney, you also have to accept that the same level of volatility could give Mr Obama a victory in the range of 350+ electoral votes. That's certainly not 1972 or 1984 territory, but it is decisive.
Just to be clear: I personally expect a regression to the mean. But the mean is on the left hand side of the graph.