Imagine if the Congress had subpoenaed all the financial records of George Washington.
Or Jackson, Jefferson, Madison.
Or Clinton, Bush, Obama.
What a sight that would be...
Alas, I cannot envision the USSC siding with the Congress. And a rational court would say they have no role in the dispute.
But in the modern era the most we can hope for is a ruling that protects POTUS under a combined umbrellas of the 4th Amendment, but mostly Executive Privilege.
A President has some limited right to privacy, and has agreement with the Courts that any oversight privilege he grants to Congress will not be harassing or in any way impede the effective execution of duties under the constitution.
Thus is the unwritten, extra-constitutional compromise of “Executive Privilege” vs “Congressional Oversight”.
When Congress and President compromised on that they made the courts the supreme arbiter of the US constitution and the superior branch of the three branches.
But there is but a SINGULAR enforcement mechanism and that is Impeachment and removal of the Executive. And none on Congress.
The “Imperial President” was the creation of the founding fathers. Awarded with immense power and discretion. As chief enforcer of the law, he was above the law. And he had sole possession of every means of enforcement at the federal level. Commander in Chief of the Army and the Navy.
His only checks were removal from office if the 2/3 of the Senate wanted it to be so. Or, his defeat at the next election. Or the House refusing to fund him.
Need to make it clear that this will set precedence for every federal level elected official and appointee.
Including SCOTUS.
The President doesn’t grant Congress its oversight privileges. They’re inherent in its roles and responsibilities.
The question is how sweeping are they and the answer is up to SCOTUS, not POTUS.