The 1964 United States Senate elections were held on November 3. The 33 seats of Class 1 were contested in regular elections. Special elections were also held to fill vacancies. They coincided with the election of President Lyndon B. Johnson by an overwhelming majority, to a full term. His Democratic Party picked up a net two seats from the Republicans. , this was the last time either party has had a two-thirds majority in the Senate, which would have hypothetically allowed the Senate Democrats to override a veto, propose constitutional amendments, convict and expel certain officials, or invoke cloture without any votes from Senate Republicans. In practice, however, internal divisions effectively prevented the Democrats from doing so. The Senate election coincided with Democratic gains in the House in the same year. In a close race in Nevada, Democratic incumbent Howard Cannon won re-election over Republican Lieutenant Governor Paul Laxalt by fewer than 100 votes. Laxalt joined Cannon in the Senate when he won Nevada's other seat in 1974. Patrick V. McNamara (D) later died April 30, 1966, and was replaced May 11, 1966, by appointee Robert P. Griffin (R), reducing Democrats' majority to 67-33. Notably, of the 35 seats up for election this year, 26 were held by Democrats, who managed to retain 25 of them. A party defending two-thirds of the seats up for election would not make net gains in the Senate again until 2012. Coincidentally, it would be the same Senate class, class 1. This is the earliest round of Senate elections in which a first-elected member is still alive. (Fred Harris, D-OK) Results summary Source: Gains, losses, and holds Retirements One Republican and two Democrats retired instead of seeking re-election. Defeats One Republican and seven Democrats sought re-election but lost in the primary or general election. Post-election changes One Democrat died on April 30, 1966, and was replaced on May 11, 1966, by a Republican appointee. Change in composition Before the elections Elections results Race summary Special elections during the 88th Congress In these special elections, the winner was seated during 1964 or before January 3, 1965; 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, 1965; ordered by state. All of the elections involved the Class 1 seats. Arizona Incumbent Barry Goldwater decided not to run for re-election