There are few political operatives more in the zeitgeist than Sean McElwee, the media-savvy pollster whose firm, Data for Progress, has been at the center of a recent debate over how Democrats should run campaigns. Over the last few years, McElwee, a socialist turned pseudo-centrist, became a leading avatar of “popularism”—the belief that Democrats should focus on poll-tested issues that win elections, and avoid activist-approved messaging that turns off the median voter. He also became a Democratic celebrity in his own right: he famously hosted a regular happy hour in New York that was incessantly profiled throughout the Trump years as an exemplar of the rowdy “new left.” Along the way, McElwee created a successful political-media brand with a big online following and relationships with Democratic power brokers that elevated Data for Progress into the big leagues alongside mainstay polling firms like GSG at a remarkable speed.