Equally untenable is the once-plausible "Bernie-Plus" hypothesis of Sen. Elizabeth Warren's (D-Mass.) campaign, in which the economic justice brigade, the social justice warriors and the party moderates would all choose her as the candidate they could live with. In practice, it turned out to be more like "Bernie-Minus": Most of the Bernie Brigades stuck with their guy, while moderates were repelled by the leftier positions she'd taken to woo his supporters.

Warren's experience suggests some other theories that probably ought to have died by now but somehow haven't. Such as the theory, already being floated Tuesday night, that Sen. Amy Klobuchar's (D-Minn.) surprising strength shows that Cory Booker and Kamala D. Harris got out too soon. Since the beginning, Klobuchar has been running as the most moderate candidate, a strategy that paid off when voters got a close look at former vice president Biden and balked. But Harris, especially, ran a variant of the Bernie-Plus strategy, which wouldn't have worked any better with more candidates in the race trying to simultaneously mop up the same limited pool of voters.

The most important theory these primaries should have killed is that of our nascent socialist revolution. That theory was plausible in 2016, when Bernie Sanders (I-Vt.) won New Hampshire with 60 percent of the vote. It is less so now that he's leaving the same state with only a quarter of its votes. Even if every one of Andrew Yang's and Warren's voters had picked him, he'd still only have gotten a bit over a third, and his polls suggest that's about where he'd be nationally, too. So what looked, four years ago, like a sharp leftward shift in the electorate now seems more like a mass protest against the party's slavish fealty to the Clintons.