An independent investigation by the FBI is all that is really being asked for, anyway.
I saw one of the talking heads making a suggestion that makes sense to me. Put the polygraph on him and be done with it. It is not a court of law, and the polygraph is routinely used for vetting top security clearances, CIA annually for example, so it shouldn't be so radical to use it to clear something up for one of the highest positions in the land which isn't subject to recurring election.
If he is not guilty of lying about groping someone long ago, a skilled polygrapher will know if he is being deceptive.