So much has been said about the alleged "pee pee tape" and I don't doubt that there may be one but I don't think Don the Con would care if that was revealed. His lemmings would probably cheer him on if they saw it.
What would bother him is people knowing about his finances or "deals" with Russia.
I think that is why we are now seeing him losing his mind on twitter again.
Those tax returns would reveal a lot IMO and if he has nothing to hide he shouldn't have held them back.