Which principle of the Constitution did that Supreme Court decision on the US vs Nixon reaffirm?

The Supreme Court decision in United States v. Nixon reaffirmed the principle of the rule of law, emphasizing that no person, not even the President, is above the law. The Court ruled that President Nixon had to comply with a subpoena to release tape recordings and documents related to the Watergate scandal, establishing that executive privilege does not grant absolute immunity from judicial oversight. This decision underscored the concept of checks and balances within the government, ensuring accountability and transparency.