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. As of 2023, this was the last time either party has had a two-thirds majority in the Senate, which allowed the Senate Democrats to override a veto, propose constitutional amendments, or convict and expel certain officials without any votes from Senate Republicans. However, internal divisions would have prevented the Democrats from having done so. The Senate election cycle coincided with Democratic gains in the House in the same year.

The 2012 United States Senate elections were held on November 6, 2012, with 33 of the 100 seats in the Senate, all Class 1 seats, being contested in regular elections whose winners would serve six-year terms beginning January 3, 2013, with the 113th Congress. Democrats had 21 seats up for election, plus 1 Independent and 1 Independent Democrat, while the Republicans had only 10 seats up for election. The presidential election, elections to the House of Representatives, elections for governors in 14 states and territories, and many state and local elections were also held on the same day.