In 1940, Clayton returned to government service in the Reconstruction Finance Corporation, then moved to the Export-Import Bank, where he worked to procure strategic materials for the United States and to deny them to Nazi Germany. After a series of administrative shuffles, Clayton found himself working under Vice President Henry A. Wallace. Disagreements between them led Clayton to resign in January 1944, only to return to government service a month later as Surplus War Property Administrator under James F. Byrnes in the Office of War Mobilization.