Quote Originally Posted by RandBlade View Post
Why 10%? Why not 5% or 15%? It's a nice round decimal figure but what's special about it?
Events, dear boy, events.

Of course something could happen in-between now and then. Your bit in bold is what I mean, if Clinton comes out and murders a small child during the debates then she probably wouldn't but as things stand she is going to win barring a change in circumstances.
The thing is, there doesn't even have to be an event. There could be zero events in the next month and a poll taken in the beginning of September will still show shifts from one taken today. Time is one of those changing circumstances of yours.