Clark Clifford served on Johnson’s President's Foreign Intelligence Advisory Board from 1961 to 1968. In 1965, General C. Westmoreland, commander of the U.S. forces in Vietnam, requested that President Johnson provide more ground troops in Vietnam and support Rolling Thunder, a bombing campaign against the North Vietnamese. Clark Clifford wrote President Johnson a letter arguing against an increase in ground troops. The now-famous letter warned that, “This could be a quagmire.” Johnson neglected to reply to Clifford’s letter but continued to seek his counsel and in 1968 named Clifford his Secretary of Defense.
