Hasan Piker has attracted millions of followers across multiple social-media platforms, making him one of the most popular left-wing streamers. He has been the subject of several flattering magazine profiles that have lingered over what they describe as his handsome looks and bodybuilder physique. Some progressives see him as their long-sought entry point into alternative media that can reach a young, mainly male, audience. But he is most important as a stand-in for a fight over whether the Democratic Party should be open to, or even dominated by, militant anti-Zionism. Although he allowed, after October 7, 2023, that “the Palestinian...