Act September 9, 1966: National Traffic and Motor Vehicle Safety Act, September 9, 1966: Highway Safety Act, October 15, 1966: National Historic Preservation Act, October 15, 1966: National Wildlife Refuge System Administration Act of 1966, October 15, 1966: Department of Transportation Act, November 2, 1966: Cuban Adjustment Act, November 3, 1966: Comprehensive Health, Planning and Service Act, Constitutional amendments July 6, 1965: Approved an amendment to the United States Constitution addressing succession to the presidency and establishing procedures both for filling a vacancy in the office of the vice president, and for responding to presidential disabilities, and submitted it to the state legislatures for ratification Amendment was later ratified on February 10, 1967, becoming the 25th Amendment to the United States Constitution Party summary The count below identifies party affiliations at the beginning of the first session of this Congress, and includes members from vacancies and newly admitted states, when they were first seated. Changes resulting from subsequent replacements are shown below in the "Changes in membership" section. Senate House of Representatives Leadership Senate President: Hubert Humphrey (D), starting January 20, 1965 President pro tempore: Carl Hayden (D) Permanent Acting President pro tempore: Lee Metcalf (D) Majority (Democratic) leadership Majority Leader and Democratic Conference Chairman: Mike Mansfield Majority Whip: Russell B. Long Caucus Secretary: George Smathers Minority (Republican) leadership Minority Leader: Everett Dirksen Minority Whip: Thomas Kuchel Republican Conference Chairman: Leverett Saltonstall Republican Conference Secretary: Milton Young National Senatorial Committee Chair: Thruston Ballard Morton Policy Committee Chairman: Bourke B. Hickenlooper House of Representatives Speaker: John W. McCormack (D) Majority (Democratic) leadership Majority Leader: Carl Albert Majority Whip: Hale Boggs Democratic Caucus Chairman: Eugene James Keogh Democratic Caucus Secretary: Leonor Sullivan Democratic Campaign Committee Chairman: Michael J. Kirwan Minority (Republican) leadership Minority Leader: Gerald Ford Minority Whip: Leslie C. Arends Republican Conference Chairman: Melvin Laird Policy Committee Chairman: John Jacob Rhodes Republican Campaign Committee Chairman: Bob Wilson Caucuses House Democratic Caucus Senate Democratic Caucus Members This list is arranged by chamber, then by state. Senators are listed in order of seniority, and representatives are listed by district. Senate Senators are popularly elected statewide every two years, with one-third beginning new six-year terms with each Congress. Preceding the names in the list below are Senate class numbers, which indicate the cycle of their election. In this Congress, Class 1 meant their term began in this Congress, requiring reelection in 1970; Class 2