I do not understand why the Republicans in the Senate do not have a competing investigation. They could subpoena people like this and ask them about collusion among the Democrats, the media, and the federal bureaucracy; and about the Democrats’ off-the-record witness coaching AKA subornation of perjury.
Most Republicans in the Senate want him gone too and probably were in on the fake Russia collusion origins or at least knew about it too but most want to continue in their positions and know the base would push them out.