The House of Representatives should establish a small, competent, select committee to determine the truth of the Ukraine matter. This committee’s investigation should be separate from those rehashing the Mueller report or looking into other Trump administration controversies
The select committee should investigate the Ukraine matter alone, with a view to discovering whether impeachable offense has been committed. (It would be fine if this were a joint select committee of the House and Senate, and that offer should be made to Mitch McConnell.)
The select committee should be given full powers of investigation and instructed to move with expedition. The House should make clear that failure by the administration to cooperate with this committee is itself a potentially impeachable offense.
This committee could hold hearings in private (on classified or sensitive matters) as well as in public.