Senate President pro Tempore Carl Hayden served as acting President of the Senate during this "odd" session of the 89th Congress due to a vacancy in the Vice Presidency of the United States until Noon on 20 January 1965 (when Vice President Hubert H. Humphrey was sworn in for a full four-year term in that office); during this same period, House Speaker John W. McCormack was next in line to the Presidency under the 1947 Presidential Succession Act.