The point of that is from U.S. v. Nixon (1974), a 9-0 decision of the Supreme Court which held that there is no Executive privilege in an impeachment trial. All requested documents must be turned over. With what Q has said about [RR] having to resign or recuse if what is in those documents is revealed, the need for conviction should not be a factor.
RR can't assert executive privilege though, and in the Nixon case, Nixon had not been impeached. The court said that it (the court) had the inherent power to enforce the subpoena, and that an unexplained claim of absolute immunity (from production of evidence for at least an in camera review) would not stand.
The underlying procedural context was criminal prosecution of people other than the president.
Since we conclude that the legitimate needs of the judicial process may outweigh Presidential privilege, it is necessary to resolve those competing interests in a manner that preserves the essential functions of each branch. ...In this case, the President challenges a subpoena served on him as a third party requiring the production of materials for use in a criminal prosecution; he does so on the claim that he has a privilege against disclosure of confidential communications. He does not place his claim of privilege on the ground they are military or diplomatic secrets. ....
... the allowance of the privilege to withhold evidence that is demonstrably relevant in a criminal trial would cut deeply into the guarantee of due process of law and gravely impair the basic function of the court. ...
We conclude that, when the ground for asserting privilege as to subpoenaed materials sought for use in a criminal trial is based only on the generalized interest in confidentiality, it cannot prevail over the fundamental demands of due process of law in the fair administration of criminal justice. The generalized assertion of privilege must yield to the demonstrated, specific need for evidence in a pending criminal trial.
US v. Nixon, 418 U.S. 683 (1974)
WHOA! That is an attention grabber. It also answers my "why bother" question about the value of impeachment if conviction is a non-starter. Impeachment is important as a last-ditch means of discovery, even if the impeachment vote fails.
I had no idea. Thanx.