The 1966 United States Senate elections were elections on November 8, 1966 for the United States Senate which occurred midway through the second (and only full) term of President Lyndon B. Johnson. The 33 seats of Class 2 were contested in regular elections. Special elections were also held to fill vacancies. With divisions in the Democratic base over the Vietnam War, and with the traditional mid-term advantage of the party not holding the presidency, the Republicans took three Democratic seats. Despite Republican gains, the balance remained overwhelmingly in favor of the Democrats, who retained a 64–36 majority. These were also the first elections held after the enactment of the Voting Rights Act of 1965. Upon Edward Brooke's election in Massachusetts, he became the first African-American U.S. Senator elected after the end of Reconstruction and the first-ever popularly elected, as Reconstruction ended before the passage of the Seventeenth Amendment to the United States Constitution. As of 2022, this is the most recent Senate election in which no House incumbents were elected to the Senate. Results summary Source: Clerk of the U.S. House of Representatives Gains, losses, and holds Retirements Two Republicans and one Democrat retired instead of seeking re-election. Defeats Four Democrats sought re-election but lost in the primary or general election. Change in composition Before the elections After the elections Race summaries Special elections during the 89th Congress In these special elections, the winner was seated during 1966 or before January 3, 1967; ordered by election date, then state. Elections leading to the next Congress In these general elections, the winners were elected for the term beginning January 3, 1967; ordered by state. All of the elections involved the Class 2 seats. Alabama Incumbent Democrat John Sparkman was easily reelected to a fourth full term. Republican challenger John Grenier received 39% of the vote, the best result that a challenger to Sparkman had ever received to that date, presaging the rise of the Republican party in Alabama after decades of Democratic dominance. Alaska Incumbent Democrat Bob Bartlett was reelected to his third (a second full) term in a landslide, defeating Republican candidate Lee McKinley in a rematch of the 1960 election. Arkansas Incumbent Democrat John L. McClellan was reelected unopposed to a fifth term in office. Colorado Republican incumbent Gordon Allott was reelected to a third term, defeating Democratic state senator and future governor Roy Romer. Delaware Republican incumbent J.