Caltech did not spell an end to Bacher's service in Washington. He served two terms as a member of the President's Science Advisory Committee (PSAC) under President Dwight D. Eisenhower, from November 18, 1953, to June 30, 1955, and from December 9, 1957, to December 31, 1959. During his first term he testified on behalf of his old friend at the Oppenheimer security hearing in 1954. During his second, he worked with James L. Fisk and Ernest Lawrence to examine how a Partial Nuclear Test Ban Treaty could be monitored.