The 1918 United States elections elected the 66th United States Congress, and took place in the middle of Democratic President Woodrow Wilson's second term. The election was held during the Fourth Party System. It was the lone election to take place during America's involvement in World War I. Republicans won control of both chambers of Congress for the first time since the 1908 election.
In an example of the six-year itch phenomenon, Republicans took complete control of Congress from the Democrats. The Republicans won large gains in the House, taking 25 seats and ending coalition control of the chamber. In the Senate, Republicans gained 5 seats, taking control of the chamber by a slim majority.
The elections were a major defeat for progressives and Wilson's foreign policy agenda, and foreshadowed the Republican victory in the 1920 election. Republicans ran against the expanded war-time government and the Fourteen Points, especially Wilson's proposal for the League of Nations. The Republican victory left them in control of both houses of Congress until the 1930 election.