The left has been traditionally defined, in its most radical form, as a movement of the working class against capitalism. What changed over the last half century? Not only has the working class not been at the forefront of radical politics, but radical politics itself has waned. Why have resistance movements become more sporadic? And what lessons can be drawn from the past to re-energize leftwing collective action in the age of Trump? Political economist David McNally talks about the past and future of radical class-based politics.