There is nothing about Congressional oversight in the Constitution
...It would be interesting to see if the Supreme Court will agree. I think it is a good argument on the face of the Constitution, but liberal judges are known for ignoring the parts of the document they don't like. I think the argument is especially strong in Trump's resistance to producing his tax return.
Sorry, Mr. Panetta, but the Constitution does not make clear anything about oversight responsibility. The theory of oversight responsibility in entirely the creation of the judicial branch and is not found anywhere within the four corners of the Constitution. Article I, Section 8, of the Constitution spells out the affirmative powers of Congress, mostly in rather restrictive, finite terms. Congress can borrow money. Congress can establish Post Offices. Congress can punish piracy. Congress can declare war. That sort of stuff. Nothing remotely close to oversight.
That’s because oversight is a so-called “implied” power — not to be confused with an “imaginary” power. It derives, we are told, from the “necessary and proper” clause included at the end of Article I, Section 8. That is also called the “elastic clause” because it has been stretched every which way to expand the power of Congress beyond recognition. Here is the full foundation on which the “oversight powers” of Congress rests:
“To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.”
Search as you will through the “foregoing powers,” however, you will not find any reference to anything remotely like oversight of the executive branch. As a matter of fact, there is absolutely no reference to the executive branch or the president in any of the preceding 17 clauses. Therefore, it cannot be “necessary and proper” for Congress to exercise oversight, nor ultimately does the power “to make all laws” needed to enforce congressional authority have any relevance to the desire of Congress to investigate the president’s private life and business.