Halperin held senior foreign policy positions in the Johnson, Nixon, and Clinton administrations.

In 1969, while he was serving on the National Security Council under Henry Kissinger, the FBI wiretapped his home phone without a warrant; he later appeared on President Richard Nixon's "Enemies List."

• He directed the Washington office of the American Civil Liberties Union (ACLU) from 1984 to 1992.

• Under President Bill Clinton, he served as director of policy planning at the U.S. Department of State from 1998 to 2001.