The New Queen of Queens

The Democratic left shows its muscle in a New York primary.

Republicans are chortling after Tuesday’s primary defeat of New York Democratic Congressional baron Joseph Crowley by Sandernista Alexandria Ocasio-Cortez, but they might want to hold the Schadenfreude. The rise of the Democratic left in this primary season portends more polarization and a more radical policy turn when the party next takes power.

Mr. Crowley’s defeat is being compared to Rep. David Brat’s primary victory over then Republican House Majority Leader Eric Cantor in 2014, and in some respects that’s true. The 56-year-old...