Serrano grew critical of Marxism and left-wing politics, instead being drawn to the Nacistas after their failed coup in September 1938. By July 1939, Serrano was publicly associating himself with the Nacista movement, now organised as the Popular Socialist Vanguard. He began writing for their journal, "Trabajo", and accompanied their leader, Jorge González von Marées, on his speaking tours across Chile. At the outbreak of the Second World War, in which Chile remained neutral, Serrano expressed support for Nazi Germany; from July 1941 he launched a fortnightly pro-Nazi publication, "La Nueva Edad". Among the magazine's regular contributors were the journalist René Arriagada, General Francisco Javier Díaz, and Hugo Gallo, who was the cultural attaché at the Italian Embassy.