Clark M. Clifford was a longtime advisor to Democratic Presidents Truman, Johnson and Carter, and held various positions in Democratic Administrations, including cabinet rank. Clifford advised American presidents on some of the crucial developments in the later half of the 20th century, including the decision to use atomic weapons at the end of World War II, the creation of the Central Intelligence Agency and National Security Agency, attempted to convince President Johnson the Vietnam War should be abandoned, and a role in the Iran Hostage Crisis. Clifford became known as a senior Democratic party insider and Washington "fix-it" man, and was caught up in the Bank of Credit and Commerce International (BCCI) affair in his twilight years.
In July 1945 Clifford attended the Potsdam Conference near Berlin with President Truman.
Throughout 1946 tension between the United States and the Soviet Union grew. In July 1946, President Harry S. Truman asked Clifford, who was serving as special counsel, to compile a list of agreements the Soviet Union had broken or were not living up to. Clifford and his assistant, George Elsey, reviewed every aspect of post World War II Soviet behaviour and American-Soviet relations.
The two aides interviewed senior officials in the U.S. Defense Department, FBI, and all agencies of government dealing with the Soviet Union. The Clifford-Elsey report put the blame squarely on Stalin for the breakdown of relations between the wartime allies. It concluded that "the Soviet Union constitutes a real menace to freedom in this world; freedom in Europe; freedom in the United States. So we must prepare for it."
According to Howard Zinn, Clifford advised Truman to connect the intervention in Greece in 1947 to a blood for oil policy—the great natural resources of the Middle East. Clifford was also one of the principal architects of the National Security Act of 1947, which unified the armed services and in which he wrote the basic legislation establishing the CIA. 
After leaving the government in 1950 Clifford practiced law in Washington, but continued to advise the White House occasionally. In 1960 he was a member of President-elect Kennedy's Committee on the Defense Establishment, headed by Stuart Symington. In May 1961 Kennedy appointed him to the President's Foreign Intelligence Advisory Board, which he chaired beginning in April 1963. After President Johnson entered office, Clifford served frequently as an unofficial counselor and sometimes undertook short-term official duties, including a trip with General Maxwell Taylor in 1967 to Vietnam and other countries in Southeast Asia and the Pacific. Clifford estimated that in the year prior to his appointment as secretary of defense he had spent about half of his time advising the president and the other half with his law firm.
Clifford was appointed by U.S. President Lyndon Johnson Secretary of Defense at the height of Johnson's escalation of the Vietnam conflict upon termination of Secretary Robert McNamara. Clifford recites in a PBS documentary on the Vietnam War that he had "turned against the war" shortly after Johnson appointed him Defense Secretary. 
Special Presidential Emissary to India
In 1980, as Special Presidential Emissary to India appointed by President Jimmy Carter, Clifford threatened the newly established regime of Ayatolla Khomeini with war for their intransigence in negotiating the release of hostages.
In 1991, Clifford's memoirs Counsel to the President (co-authored with Richard Holbrooke) were published just as his name was implicated in the unfolding Bank of Credit and Commerce International (BCCI) scandal. The bank, with Clifford as its chairman, was called First American Bankshares and became the largest in Washington. Robert Morgenthau, the district attorney in New York City, disclosed that his office had found evidence that the parent company of Clifford's bank was secretly controlled by BCCI. The district attorney convened a grand jury to determine whether Clifford and his partner, Robert Altman, had deliberately misled federal regulators when the two men assured them that BCCI would have no control.
Clifford's predicament worsened when it was disclosed he had made about $6 million in profits from bank stock that he bought with an unsecured loan from BCCI. A New York grand jury handed up indictments, as did the Justice Department. Clifford's assets in New York, where he kept most of his investments, were frozen.
The "Report to the Committee on Foreign Relations United States Senate" led by Senators John Kerry and Hank Brown noted that a key strategy of "BCCI's successful secret acquisitions of U.S. banks in the face of regulatory suspicion was its aggressive use of a series of prominent Americans," Clifford among them.  Clifford, who prided himself on decades of meticulously ethical civic conduct, summed his predicament up when he told a reporter from the New York Times, "I have a choice of either seeming stupid or venal." Indictments against Clifford had been set aside because of his failing health.
- Oral History Interviews with Clark M. Clifford, Truman Presidential Library.
- Vietnam: A Television History, (1983). Transcript retrieved from PBS.org 13 July 2007.
- The BCCI Affair, A Report to the Committee on Foreign Relations, 102d Congress 2d Session Senate, December 1992.