Larry Sabato emphasizes them:
Almost everything can change, and frequently does, during the course of the election year. The economy can get decidedly better or worse. International crises can pop up — or peace can break out. Unexpected scandals can engulf one or both major party candidates. One or more independents or third-party candidates may prove influential in the presidential tally. So enjoy the primaries, savor the polls, watch the campaigns like a multiring circus. But don't believe you really know anything about November.
And while you're in the thick of it, there's always time for some singing:
He doesn't look too rattled, does he?
The Dish 