Why has David Horowitz devoted so many years and words to expounding the radical left-wing mind? It started in the mid-1980s with Horowitz and collaborator Peter Collier speaking and writing about their “Second Thoughts” of being 1960s radicals. Horowitz turned a microscope upon himself in 1997 with Radical Son, a memoir of Red Diaper childhood and militant adulthood amidst the Black Panthers and Ramparts magazine until he retreated out of disgust at the violence, white guilt, and indifference to the fate of South Vietnam after US troops withdrew. Several books followed, including The Politics of Bad Faith (2000), Left Illusions (2003), One-Party Classroom (2009), and now Radicals: Portrait of a Destructive Passion, which “is perhaps the last [Horowitz] will write about a subject that has occupied [him] in one way or another over the course of a lifetime.”

The radical mind is a duplicitous, self-deceiving, willful, and scheming formation, one that exercises enough pull on certain groups and figures and policies in the United States to merit ongoing diagnosis. That’s the assumption underlying Horowitz’s work, indeed, his whole life—that is, once he broke with the left after uncovering a murder committed by Black Panther leaders whom he had theretofore glorified. Radicalism has its political content, he agrees, but it marks a pathological condition as well. If it were only political, it would advocate for a single-payer healthcare system, a more steeply progressive income tax, and other policies expanding state control. People demand those reforms, of