Define executive privilege and explain why executive privilege was restricted during President Nixon's administration.

Executive privilege allows the President to withhold information from government actors and/or the general public, primarily based on national security concerns. Before President Nixon, executive privilege was largely unquestioned and unchecked.
In investigating the Watergate scandal, Special Prosecutor Leon Jaworski subpoenaed tapes of Nixon's conversations related to the scandal. In 1974's United States vs. Nixon, the President sought to invoke executive privilege to avoid turning over the tapes. The district court judge in the case found in favor of Jaworski, and Nixon appealed to the Supreme Court.
The Supreme Court unanimously affirmed that executive privilege has certain limits, ordering Nixon to turn over the evidence as part of a lawful investigation. Due to Nixon's attempt to use executive privilege to conceal his involvement in Watergate, and the subsequent SCOTUS ruling, laws have been passed in order to challenge executive privilege in the public interest. One such law is the Freedom of Information Act.