How severe are the Democrats’ divisions? The factions seem nowhere near as tribal and mutually incomprehensible as the Republican crackup; most Sanders supporters I met said they respected Clinton, even if they didn’t trust her, and Clinton supporters said they get where the Sanders people are coming from.

But in one respect, the Democratic revolt is worse, because the party didn’t see it coming. Republicans have known for years they had problems, a restive base they couldn’t control. Democrats are just now finding out.

It’s still a mystery why, exactly, Clinton lost control of this race. As of mid-December, she seemed to be sitting pretty, winning the debates, leading in Iowa, and catching up to Sanders in New Hampshire. But sometime around the new year that changed, and Sanders surged.

Was it Trump’s insults, Sanders’s ads, a fluke of the polls? Nobody could really say. But the professionals behind Team Clinton reacted to this surprise development with all the grace and equanimity of a mule that’s just been bitten by a deerfly and is thrashing wildly around. Clinton attacked Sanders with wild implausibility, insisting he was both too left-wing to win and not liberal enough on certain issues, primarily gun control. When Sanders lashed rather mildly back, her campaign flew off the handle, accusing him in dire terms of a viciousness ill-befitting his gentle reputation. Perhaps there are Iowa Democrats who were gravitating to Sanders until they heard he had “gone negative,” and stopped in their tracks; I have yet to meet them.