President Richard Nixon launched the War on Drugs for one specific reason: to decimate his perceived political enemies—the anti-war left. That's according to an anecdote in a lengthy cover story for Harper's, in which journalist Dan Baum recounts an interview he conducted with John Erlichman, a former Nixon staffer who was jailed for one year due to his involvement in the Watergate scandal. Unprompted, Erlichman confessed the true purpose of federal drug prohibition: “You want to know what this was really all about?” he asked with the bluntness of a man who, after public disgrace and a stretch in federal...