He was a staunch advocate of the United States' entry into World War I and spoke in favor of increased military preparedness via universal military service as the president of the National Security League in 1916. He criticized President Woodrow Wilson for inaction at the invasion of Belgium and sought the Republican nomination for U.S. Senate against William M. Calder. Bacon continued to push for a stronger national defense as well as a protective tariff that could be used for the mobilization of industry in case of war. Although he had support from former president Theodore Roosevelt and Elihu Root, Bacon lost the race by about 9,000 votes and pledged to support Calder. He was named as the candidate of the American Party but withdrew on account of his pledge to Calder.