Rein Vander Zee later served as assistant to Senator Hubert Humphrey when he became Democratic whip in 1961. Vander Zee later served as assistant secretary of the majority, where he supervised the Democratic cloakroom and assisted Majority Leader Mike Mansfield and Democratic Secretary Bobby Baker. Having previously worked on the staff of Iowa representative Steven V. Carter, Vander Zee joined Humphrey's presidential campaign during the 1960 primaries, including the decisive West Virginia primary between Humphrey and John F. Kennedy. He then acted as an advance man for the Kennedy-Johnson ticket before joining the Senate staff in 1961. After leaving the Senate staff in 1964, he remained in Washington as a lawyer and lobbyist, and worked for Johnson and Humphrey during the 1968 campaign before returning to Texas in 1970. His oral history recounts the personalities and politics of the era among the senators, the staff, and presidential administrations of John Kennedy and Lyndon Johnson.