Chester Cooper is well known as the author of The Lost Crusade: The United States in Vietnam (1970) but his role as a Vietnam policymaker ? though important - has been overlooked. He worked for the CIA and then for the National Security Council under Kennedy and Johnson, growing deeply disenchanted with American policy after the murder of President Diem in 1963. After trying to halt the escalation of the US role in Vietnam, he joined the State Department to seek a negotiated peace. Despite his best efforts, the results were sparse. In exploring Cooper?s involvement in the Vietnam War, the article fills a gap in the literature and touches on questions of military strategy, decision-making, the prospects of a negotiated peace, and internal dissent.