Statistics whiz Andrew Gelman considers various theories.
The polls weren’t all that wrong, but just enough in the key states. Trump was running a cheapskate campaign, so he didn’t try to notch better national vote totals by appealing to California, Texas, or New York. In the battleground states where he concentrated his effort, he did strikingly well.
Moreover, the amount of political violence in America over the last twelve months was very high by recent historical standards, with perhaps 95% of it coming from the anti-Trump half of the spectrum (and more of it coming tonight).
I was at a dinner party in one of the more conservative parts of Southern California awhile ago, the San Gabriel Valley suburb of Sierra Madre. One guest went on a long rant about how Trump appealed to stupid people, unlike us here at the table. Another guest tossed in witty asides that the anti-Trump ranter took as support, but when carefully analyzed clearly revealed a subversive pro-Trump stance.
Then I went to another dinner party the next week in liberal Sherman Oaks where the exact same thing happened: a long politically correct rant subtly subverted by another guest’s witty but ambiguous wisecracks.
I had never met the wisecracking guest, a 40-something doctor, before. When the topic of South Korea came up, he mentioned that he had spent some time there due to “an excess of patriotism.” I eventually figured out from his self-deprecating jokes that when he’d graduated from high school in the late Reagan Era, he’d enlisted in the Marines.
My guess is that Donald Trump is President-Elect because enough witty people in the suburbs of Detroit, Milwaukee, Philadelphia, Cleveland, and Miami held their tongues until they got into the privacy of the voting booth.