If classified information is provided to the Congress or Courts it remains in the purview of the Executive. It is only provided under the binding condition that it be safeguarded by means appropriate to its classification.
Providing written information to the Congress only prevents Schiff for Brains from leaking it. He can do what he wishes with oral testimony as such testimony then belongs to the Congress.
There is absolutely nothing he can do to prevent declassification of Executive Branch material.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)