I've long held a working theory that US voters are completely predictable in Presidential elections.
The idea is that Americans almost invariably tend to swing wildly every few election cycles, voting for the candidate who is as close to the opposite of the current guy as possible.
Let's go back a few decades to, say, Jimmy Carter.
In 1976, the country was sick and tired of the corruption, scandal, and disgrace of Richard Nixon's administration (which at that point had been inherited by Gerald Ford).
Jimmy Carter was pretty much the opposite of Richard Nixon– a youthful outsider versus an aging crony.
After four years of economic disaster, Americans swung in the opposite direction from Carter, choosing an older, polished conservative in Ronald Reagan who represented strength and stability.
That trend lasted for twelve years– two terms with Reagan, and one term with his successor George HW Bush, after which the country swung in the other direction again– to Bill Clinton.
Clinton was another young, energetic liberal, pretty much the opposite of the elderly, curmudgeonly Bush.
After eight year of Clinton and his personal scandals, the country swung again to George W. Bush, a God-fearing, fundamental conservative who wouldn't cheat on his wife. He represented Clinton's opposite.
And after eight years of war and economic turmoil, the country swung once again to Bush's opposite– a youthful, charismatic, black outsider.