As far-flung as these incidents were, they have something crucial in common. Like the organizations that opposed the Multnomah County Republican Party’s participation in the 82nd Avenue of Roses Parade, these activists appear to be linked to a movement called “antifa,” which is short for antifascist or Anti-Fascist Action. The movement’s secrecy makes definitively cataloging its activities difficult, but this much is certain: Antifa’s power is growing. And how the rest of the activist left responds will help define its moral character in the Trump age.
Antifa’s perceived legitimacy is inversely correlated with the government’s. Which is why, in the Trump era, the movement is growing like never before. As the president derides and subverts liberal-democratic norms, progressives face a choice. They can recommit to the rules of fair play, and try to limit the president’s corrosive effect, though they...