He supported the isolationist Neutrality Acts of the 1930s but wanted and sponsored more severe bills designed to renounce all traditional neutral "rights" and restrict and prevent any action by the President that might cause the United States to be drawn into war. He was one of the most effective of the diehard isolationists in the Senate. Except for advocating aid to Finland after the Soviet invasion of that country and urging a quid pro quo in the Far East to prevent a war with Japan over the Manchuria-China question, his position was consistently isolationist.
In mid-1939 he introduced legislation nullifying the 1911 Treaty of Navigation and Commerce with Japan and urged that the administration to negotiate a new treaty with Japan recognizing the status quo with regard to Japan's occupation of Chinese territory.