UNITED STATES V. NIXON
Mr. Chief Justice Burger delivered the opinion of the Court. This litigation presents for review the denial of a motion, filed
behalf of the in the case of United States v. Mitchell et al., to quash a third-party subpoena duces tecum...direct the President to produce certain tape recordings and documents relating to his conversations with aides and advisers. The court rejected the President's claims of absolute executive privilege, of lack of jurisdiction.... A. ...we turn to the claim that the subpoena should be quashed because it demands "confidential conversations between a President and his close advisors that it would be inconsistent with the public interest to produce." The first contention is a broad claim that the separation of powers doctrine precludes judicial review of a President's claim of privilege. The second contention is that if he does not prevail on the claim of absolute privilege, the court should hold as a matter of constitutional law that the privilege prevails over the subpoena duces tecum.
In the performance of assigned constitutional duties each branch of the Government must initially interpret the Constitution, and the interpretation of its powers by any branch is due great respect from the other. The President's counsel the Constitution as providing an absolute privilege of confidentiality for all Presidential communications. Many decisions of this Court, however, have unequivocally reaffirmed the holding of that "it is emphatically the province and duty of the judicial department to say what the law is."
No holding of the Court has defined the scope of judicial power specifically related to the enforcement of a subpoena for confidential Presidential communications for use in a criminal prosecution, but other exercises of powers by the Executive Branch and the Legislative Branch have been found invalid as in conflict with the Constitution. In a series of cases, the Court interpreted the explicit immunity conferred by express provisions of the Constitution on Members of the House and Senate by the Speech or Debate Clause. Since this Court has consistently exercised the power to construe and delineate claims arising under express powers, it must follow that the Court has authority to interpret claims with respect to powers alleged to derive from enumerated interpret claims with respect to powers.
...Notwithstanding the deference each branch must accord the others, the "judicial Power of the United States" vested in the federal courts by can no more be shared with the Executive Branch than the Chief Executive for example, can share with the Judiciary the veto power, or the Congress share with the Judiciary the power to override a Presidential veto. Any other conclusion would be contrary to the basic concept of separation of powers and the checks and balances that flow from the scheme of a tripartite government. We therefore reaffirm that it is the province and the duty of this Court "to say what the law is" with respect to the claim of privilege presented in this case.
http://usinfo.state.gov/usa/infousa/facts/democrac/72.htm