My guess, Mueller has either issued or will issue an subpeona for Trump to testify. Since they are doing that, they will withhold documents he ordered surrendered to Congress as that would obstruct Mueller’s probe.
When he says that, a Marshall should show up and hand him his pink slip announcing in a loud voice, you are fired immediately, don’t go back to your office as we are here to escort you out of the building and right over the scaffold being constructed at the Navy Yard.