[236]

Ratification debate and defeat
Wilson returning from the Versailles Peace Conference, 1919
Ratification of the Treaty of Versailles required the support of two-thirds of the Senate, a difficult proposition given that Republicans held a narrow majority in the Senate after the 1918 U.S. elections.[237] Republicans were outraged by Wilson's failure to discuss the war or its aftermath with them, and an intensely partisan battle developed in the Senate. Republican Senator Henry Cabot Lodge supported a version of the treaty that required Wilson to compromise. Wilson refused.[237] Some Republicans, including former President Taft and former Secretary of State Elihu Root, favored ratification of the treaty with some modifications, and their public support gave Wilson some chance of winning the treaty's ratification.[237]
The debate over the treaty centered around a debate over the American role in the world community in the post-war era, and senators fell into three main groups. The first group, consisting of most Democrats, favored the treaty.[237] Fourteen senators, mostly Republicans, were known as the "irreconcilables" as they completely opposed U.S. entrance into the League of Nations. 