United States v. Nixon (1974)
During the trial of those who had been accused of the 1972 break-in of the Democratic National Committee's headquarters at the Watergate Complex, it was discovered that President Nixon had been taping conversations in the Oval Office. A federal grand jury sitting in the District of Columbia investigating Watergate indicted former Attorney General John Mitchell and six other individuals, alleging conspiracy to defraud the United States and obstruction of justice. The Special Prosecutor, Leon Jaworski, also persuaded the grand jury to name President Nixon as an "unindicted co-conspirator" (because he had reservations as to whether a sitting President could be indicted without first being impeached and removed from office). Thus, on April 18, 1974, a subpoena was issued ordering Nixon to produce and hand over the tape recordings of conversations, and other materials in his possession that would be relevant to the upcoming trial of those indicted. However, President Nixon refused to turn these materials over on grounds of "executive privilege."
The Supreme Court heard the case. Nixon's lawyer argued that the issue at stake was the philosophy of separation of powers while the United States prosecutor argued that if the President was wrong in how he interprets the Constitution, who was going to tell him and set him straight? The Court unanimously decided against the President, ruling that neither the great honor bestowed upon the presidency nor the doctrine of a "separation of powers" gave the president an absolute privilege of immunity from a court's demand for evidence in a criminal trial. Thus, the constitutionality of the subpoena issued was affirmed and on April 30th, the President released to the public, tapes of White House conversations relating to the Watergate break-in. Within three weeks, Nixon resigned the presidency.