Just browsing over the Supreme Court decision of Executive Order No. 464.
Some choice cuts from it:
Congress undoubtedly has a right to information from the executive branch whenever it is sought in aid of legislation. If the executive branch withholds such information on the ground that it is privileged, it must so assert it and state the reason therefor and why it must be respected.
The infirm provisions of E.O. 464, however, allow the executive branch to evade congressional requests for information without need of clearly asserting a right to do so and/or proffering its reasons therefor.
By the mere expedient of invoking said provisions, the power of Congress to conduct inquiries in aid of legislation is frustrated. That is impermissible. w]hat republican theory did accomplish…was to reverse the old presumption in favor of secrecy, based on the divine right of kings and nobles, and replace it with a presumption in favor of publicity, based on the doctrine of popular sovereignty. (Underscoring supplied)
Otherwise, we shall not have merely nullified the power of our legislature to inquire into the operations of government, but we shall have given up something of much greater value – our right as a people to take part in government.
You may also want to read a comment I made when they passed that executive order.