Jeff Greenfield has been reporting and analyzing politics for 40+ years. Here he writes for Yahoo News to say that, at this point, predicting the outcome of the November election is folly.
Greenfield's variables: the economy of course, foreign affairs, a career-sinking gaffe, emergence of a Willie Horton or Swift Boat ad buy, etc. He calls these "black swans," oddball things that happen, often outside the control of either campaign.
This year many speculate on the imponderable impact of an early autumn attack on Iran by Israel (or the U.S or both). Not knowing is what keeps the game interesting, right?