In its most basic and simplest form the President's refusal to produce documents and refusal to allow testimony is a refusal to account for the money Congress provides. That accounting is called an audit.
Congress has the absolute, unconditional right to know exactly what the money they provide the President is producing. How is that money being used? What, exactly, is being done with it? Every document, every decision, every action by the President and his administration is paid for by Congress.
The reality is that there is no so-called "Constitutional Crisis". All Congress has to do is refuse to provide any more money until the President fully accounts for what he has already spent.
Obviously he will refuse. He has to. Otherwise he will undoubtedly will be impeached, possibly convicted and jailed.
A long time ago the American people decided to aggressively eliminate politics from the administration of justice and from routine operations of the government. That is why we created the civil service system among many other laws, regulations and well established traditions.
Bush has destroyed those firewalls between politics and justice, between politics and the operations of virtually every government agency and between politics and religion. He is like a really nasty virus running amok on an already flakey computer.
Right now the President claims that Congress is conducting over 300 investigations, i.e. audits, and as far as I can tell he refuses to cooperate with a single one of them. Imagine how long a bank manager or stock broker would last if they refused to cooperate with an audit of their accounts.
The President's claim of "executive privilege" is simply an overblown refusal to allow an audit.
All but the most dimwitted American recognizes that nobody can refuse an audit by the proper authority.
I think that the overwhelming majority of Americans would back a Congressional refusal to provide money for government operations until the President cooperates in an audit of how the money already spent has been used.
Shut it down. We demand an audit.
The Republicans will become unhinged. The response is, "Audit!". Obviously the corporate media will go ballistic. The response is, "Audit!". The talking heads will spin so fast the drool will fly from coast to coast. The response is, "Audit!". The fundies know it means the end of their hand in the till so the preachers will scream. The corporations won't get their government checks and they will froth at the mouth. The response is, "It's the Audit, stupid!".
But all the evil things that will happen, happen because the President refuses to allow an audit.