The 1880–81 United States Senate elections were elections that coincided with the presidential election of 1880, and had the Democratic Party lose five seats in the United States Senate. The newly elected Readjuster senator William Mahone caucused with the Republicans, and the Republican Vice President's tie-breaking vote gave the Republicans the slightest majority. All of that changed on September 19, 1881, when Vice President Chester Arthur ascended to the Presidency and the Senate became evenly divided for the first time in history.