The term “executive privilege” was not used until the 1950s. The doctrine’s contours were unclear until a 1974 Supreme Court case. In U.S. v. Nixon, President Richard Nixon was ordered to deliver tapes and other subpoenaed materials to a federal judge for review. The justices ruled 9-0 that a president’s right to privacy in his communications must be balanced against Congress’ need to investigate and oversee the executive branch.
U.S. v. Nixon is also widely understood to mean that executive privilege cannot be used to cover up wrongdoing. That view was endorsed by current U.S. Attorney General William Barr during his Senate confirmation hearing.
One lesson of U.S. v. Nixon is that an executive privilege claim is particularly weak when Congress has invoked its power to remove a president from office through impeachment, said Frank Bowman, a law professor at the University of Missouri.
In the impeachment context, “virtually no part of a president’s duties or behavior is exempt from scrutiny,” Bowman said.