In 1968, he signed the "Writers and Editors War Tax Protest" pledge, vowing to refuse tax payments in protest against the Vietnam War. After leaving "Sing Out!" in 1968, Silber became cultural editor of the independent radical newsweekly, "The Guardian" and also its film critic. He began to write on more directly political subjects, specializing in analysis of both national and international developments and developing a broad and appreciative readership. He became the "Guardian's" executive editor in 1972 and led it into the milieu of the New Communist Movement. Factional disagreements led to a split within the "Guardian" staff, and Silber left the newspaper in 1979, moving to California to join the leadership of a current within US Marxism known as the "rectification movement" and he affiliated with the Line of March.