In late May, an alliance of anti-Putin partisans used Ukrainian territory to launch a stunning incursion into western Russia. Spearheaded by the Russian Volunteer Corps, or RVC, and its leader Denis Kapustin, a wanted neo-Nazi and ex-soccer hooligan, the assault exposed just how vulnerable Russia had become to attacks since its invasion of Ukraine. For years, Kapustin has maintained public links with two notorious American neo-Nazis: Robert Rundo, the founder of the street fighting gang Rise Above Movement, and Christopher Pohlhaus, an ex-Marine and leader of a group that terrorizes drag events in the U.S. While Kapustin has been a...