Baker presided over the U.S. military's participation in World War I. He selected General John J. Pershing to command the American Expeditionary Forces, which he insisted act as an independent unit. He left office in 1921 and returned to BakerHostetler, the legal practice he co-founded. He served as an attorney in "Village of Euclid v. Ambler Realty Co.", a landmark case that established the constitutionality of zoning laws. He was a strong supporter of the League of Nations and continued to advocate American participation in the League during the 1920s. Beginning in 1928, he served as a member of the Permanent Court of Arbitration. He was a candidate for the presidential nomination at the 1932 Democratic National Convention, but the convention chose Franklin D. Roosevelt.