‘The basic question involved with this is whether this is a correct action for the Office of the President of the United States of America to take, in order to preserve the separation of powers ... or not.’
As I understand it this guy was subpoenaed to appear and is now refusing. It has nothing to do with separation of powers and everything to do with contempt of Congress. He has to appear if only to take the Fifth, as I understand it.
This an investigative committee and if it holds him in contempt his butt can be hauled to jail. If he was not subpoenaed then I guess he could refuse.
I posted this earlier for the information contained, which summarizes this in a small amount of space and gives some history for other Presidents ...
Executive Privilege
http://www.wikipedia.org/wiki/Executive_privilege
In the United States government, executive privilege is the power claimed by the President of the United States and other members of the executive branch to resist certain subpoenas and other interventions by the legislative and judicial branches of government to access information and personnel relating to the executive branch. The concept of executive privilege is not mentioned explicitly in the United States Constitution, but the Supreme Court of the United States ruled it to be an element of the separation of powers doctrine, and/or derived from the supremacy of executive branch in its own area of Constitutional activity.
The Supreme Court confirmed the legitimacy of this doctrine in United States v. Nixon, but only to the extent of confirming that there is a qualified privilege. Once invoked, a presumption of privilege is established, requiring the Prosecutor to make a “sufficient showing” that the “Presidential material” is “essential to the justice of the case” (418 U.S. at 713-14). Chief Justice Burger further stated that executive privilege would most effectively apply when the oversight of the executive would impair that branch’s national security concerns.
[ ... see the rest of the article at link ... ]
Look at the “process” that one has to go through to get an idea of what has to happen ...
The way I read it is that once Executive Privilege is claimed, then the courts will have to sort it out (from my earlier post ... ).