> Testimony or private records of the President or his advisers probing such conduct may not be admitted as evidence at trial.
And the 'smoking gun' implicating Nixon:
> Nixon then released the tapes six days later. On one tape was the so-called "smoking gun," showing that six days after the break-in Nixon had tried to use the CIA to block the FBI investigation of the burglary.
IANAL, but my understanding is under this ruling those tapes would have never been made permissible evidence in court. Giving orders to the CIA is certainly an official act, as much as granting pardons is, and this court has established the examination of said motives is out-of-scope:
> In dividing official from unofficial conduct, courts may not inquire into the President’s motives. Such a “highly intrusive” inquiry would risk exposing even the most obvious instances of official conduct to judicial examination on the mere allegation of improper purpose. Fitzgerald, 457 U. S., at 756. Nor may courts deem an action unofficial merely because it allegedly violates a generally applicable law.