Until now, hard-left influencer Hasan Piker was perhaps best known for appearing to use an electric shock collar on his dog during a livestream. Now he's making news again—for addressing the College Democrats of America convention dressed as Mao Zedong.

Piker has called Mao "one of the great leaders of this world." Yet Mao's policies are widely estimated to have caused the deaths of between 40 and 70 million people.

Had Piker shown up dressed as Hitler, the outrage would have been immediate—and rightly so. Mao deserves no better. 

Piker’s appearance, and his denunciation of mainstream Democrats for compromising with so-called fascists, reflects the extremist rhetoric gaining ground on the left. Unless Democrats of good faith confront that radical fringe, their party risks losing itself. Let's hope it's not already too late.