In 1966, he ran for Congress while still holding his State Senate seat, which he resigned upon winning the federal office.

Sandman was on the House Judiciary Committee when it considered articles of impeachment against President Richard Nixon.

Despite Sandman's change of heart on impeachment, his reputation was severely tarnished by his performance in the televised hearings.

He was soundly defeated by Democrat William J. Hughes, his opponent in 1974, in an election that Sandman described as "not a Republican year"[6] Following his defeat in his reelection bid for Congress, Sandman was approached by Vice President Nelson Rockefeller to join the Ford administration in various capacities including an ambassadorship of his choosing, Sandman declined and instead opted to accept Governor Thomas Kean's invitation to be appointed to the bench of the Superior Court of New Jersey.

[7] In the 2019 Apple TV+ series, For All Mankind, actor Saul Rubinek played Sandman in a fictional storyline about NASA, Wernher von Braun and other space issues.