The people were the most surprised by Mr. Trump’s victory were those who were not considering all of the evidence. The last estimate I remember from 538 was that Clinton had roughly a 75% chance of winning. That is, by no means, a sure thing.
Last summer, the United Kingdom voted to leave the European Union in what bettors, financial markets and the London-based media regarded as a colossal upset. Reporters and pundits were quick to blame the polls for the unexpected result. But the polls had been fine, more or less: In the closing days of the Brexit campaign, they’d shown an almost-even race, and Leave’s narrow victory (by a margin just under 4 percentage points) was about as consistent with them as it was with anything else. The failure was not so much with the polls but with the people who were analyzing them.