If you think this issue is clear cut: either that Bush has no power to prevent the testimony of his staff, or that Bush has just such a power, as Mr. Snow asserted, think again.
There is one SCOTUS ruling directly bearing on executive privilege.
United States v. Nixon 1974
Neither the doctrine of separation of powers nor the generalized need for confidentiality of high-level communications, without more, can sustain an absolute, unqualified Presidential privilege of immunity from judicial process under all circumstances. See, e. g., Marbury v. Madison, 1 Cranch 137, 177; Baker v. Carr, 369 U.S. 186, 211 . Absent a claim of need to protect military, diplomatic, or sensitive national security secrets, the confidentiality of <418 U.S. 683, 685> Presidential communications is not significantly diminished by producing material for a criminal trial under the protected conditions of in camera inspection, and any absolute executive privilege under Art. II of the Constitution would plainly conflict with the function of the courts under the Constitution. Pp. 703-707.
5. Although the courts will afford the utmost deference to Presidential acts in the performance of an Art. II function, United States v. Burr, 25 F. Cas. 187, 190, 191-192 (No. 14,694), when a claim of Presidential privilege as to materials subpoenaed for use in a criminal trial is based, as it is here, not on the ground that military or diplomatic secrets are implicated, but merely on the ground of a generalized interest in confidentiality, the President's generalized assertion of privilege must yield to the demonstrated, specific need for evidence in a pending criminal trial and the fundamental demands of due process of law in the fair administration of criminal justice. Pp. 707-713.
6. On the basis of this Court's examination of the record, it cannot be concluded that the District Court erred in ordering in camera examination of the subpoenaed material, which shall now forthwith be transmitted to the District Court. Pp. 713-714.
http://caselaw.lp.findlaw.com/scripts/getcase.pl?navby=case&court=us&vol=418&page=683Unfortunately while this ruling, one of the clearest on the issue of executive privilege, states that there is no absolute power, the limitation it places is defined by a criminal investigation.
Notes from an NPR interview of Columbia Law professor Michael Dorf.
http://www.npr.org/templates/story/story.php?storyId=8997407Court has only recognized a qualified privilege. (US v Nixon again.)
Course of action.
1. Contempt of Congress.
Congress issues subpoenas. Rove and Miers refuse to recognize them. Congress votes on a contempt of congress bill against them. This then gets referred to the Justice Department for prosecution. The Justice Department, headed by one Mr. Gonzales, does absolutely nothing.
2. Direct to court.
Congress issues subpoenas. Rove and Miers refuse to recognize them. Leahy, for example, goes to court to argue against the unwritten power of executive privilege in this case. The court either hears his case or refuses to hear his case. Historically, the case of US v Nixon being the exception, the courts have ducked this issue.
Gonzales. As a cabinet officer Gonzales cannot claim executive privilege for himself, by tradition he must testify, but could refuse to answer specific question by asserting executive privilege.
Nobody really knows how this is going to play out. The stench of impropriety here is going to make it very difficult for the supreme court, if it does hear this case, to hold that executive privilege, which by tradition has been restricted to areas of national security, can be used to obstruct an investigation into a matter that is clearly not at all involved with national security. The implications of such a ruling in favor of Bush would be that the president and his staff can conduct a criminal conspiracy within the confines of the executive branch immune from any interference from other branches of government.