418 u.s. 643 (1974)

It’s a quirk of history to be savoured that Special Council Robert Mueller’s testimony before the US Congress was delayed and coincides with the forty-fifth anniversary of the Supreme Court handing down its unanimous decision on The United States v. Nixon.
Even the president’s own attorney, requesting that the authorities drop their request to subpoena the incriminating tapes by dint of executive privilege, stated that, “The president wants me to argue that he is as powerful a monarch as Louis XIV, only four years at a time, and is not subject to the processes of any court in the land except the court of impeachment.” The Supreme Court held, however, that Nixon could be compelled to hand over evidence in a criminal trial that is demonstrably relevant and that no person is above the law. In lieu of impeachment, Nixon resigned two weeks later, ultimately pardoned for his wrongdoings by his vice-president and successor Gerald Ford in September of the same year.