The lesson is this: When a field is divided 20 different ways among a bunch of candidates who cancel each other out, the candidate who makes a loud, emotional or even outrageous appeal can incite enough of a disenchanted plurality to win.
Now, I know what Democrats are going to say to this, which is that their electorate believes in governing experience, and they don’t have a candidate who is as odious as Trump. No one’s going to solidify a quarter of the Democratic vote by preaching bigotry and failing to demonstrate even a passing knowledge of policy.
Which may be true (I’m less sure about that last one), except that the party does have its own brand of angry populism, and it’s just as rage-filled and backward-looking as populism on the right. It’s anti-trade, isolationist and nostalgic. It offers no way forward that doesn’t wind its way back through the 1930s.