He founded the leftist Partido Revolucionario Dominicano (PRD) in 1939 and was exiled during the dictatorship of Rafael Trujillo. After the latter’s assassination he returned (1961) to the Dominican Republic and was elected President (1962–63) in the first free elections for nearly forty years. He introduced sweeping liberal and democratic reforms, but after nine months in office was overthrown by rightist military leaders with the backing of the Church, of landowners, and of industrialists. His supporters launched their revolt in 1965, a movement which prompted a military intervention by the USA. In 1966 he was defeated for the presidency by Joaquin Balaguer, who had heavy US backing.