What principle did United States v. Nixon establish regarding executive privilege?

United States v. Nixon established that executive privilege cannot be used to withhold evidence in criminal trials. This landmark case arose during the Watergate scandal when President Nixon attempted to use executive privilege to avoid subpoenaing tapes of his conversations relevant to the investigation. The Supreme Court ruled that while the president has a degree of executive privilege, it is not absolute and does not extend to withholding evidence in a criminal trial, particularly when the evidence is necessary for a fair legal proceeding. This decision underscored the principle that no one, not even the president, is above the law, affirming the judiciary's role in ensuring justice.

This ruling emphasized the balance of power among the branches of government, specifically that the executive branch cannot use privilege to obstruct judicial processes in criminal cases. The other options do not accurately capture this critical aspect of the ruling, as they misinterpret the scope and limitations of executive privilege as defined by the Supreme Court in this case.