Seems to me as Commander and Chief, Trump can address this legally and publicly
Issue an Ex. Order stating that all Fed. Agencies must and will immediately comply to any and all Congressional Supaenas. Failure to comply will constitute a failure to perform your duties and will result in termination of Employment and possible prosecution for obstruction.
If these were normal times I have no doubt Trump would do what you expressed, except I suspect he understands that he has little to no support & once he issued this warning it would not be acted upon & then the true nature of what he’s up against would be exposed. If I were him I would do it anyway. Expose this for what it is.
Wray to Sessions to Trump.
I see nothing being done to correct the problem.