Wallace initially remained active in politics following the 1948 campaign, and he delivered the keynote address at the 1950 Progressive National Convention. In early 1949, Wallace testified before Congress in the hope of preventing the ratification of the North Atlantic Treaty, which established the NATO alliance between the United States, Canada, and several European countries. He became increasingly critical of the Soviet Union after 1948, and he resigned from the Progressive Party in August 1950 due to his support for the UN intervention in the Korean War. After leaving the Progressive Party, Wallace endured what biographers John Culver and John Hyde describe as a "long, slow decline into obscurity marked by a certain acceptance of his outcast status". In the early 1950s, he spent much of his time rebutting attacks by prominent public figures like General Leslie Groves, who claimed to have stopped providing Wallace with information regarding the Manhattan Project because he considered Wallace to be a security risk. In 1951, Wallace appeared before Congress to deny accusations that in 1944 he had encouraged a coalition between Chiang Kai-shek and the Chinese Communists. In 1952, he published an article, "Where I Was Wrong", in which he repudiated his earlier foreign policy positions and declared the Soviet Union to be "utterly evil".