部分的核実験禁止条約
After his gubernatorial defeat, Harriman became a widely respected foreign policy elder within the Democratic Party. He helped negotiate the Partial Nuclear Test Ban Treaty during President John F. Kennedy's administration, and was deeply involved in the Vietnam War during the Kennedy and Lyndon B. Johnson administrations. After Johnson left office in 1969, Harriman became affiliated with various organizations, including the Club of Rome and the Council on Foreign Relations.