The more he says it the more she has to deny it. If she denies it then Trump brings out witnesses to prove her a liar.
Hillary’s best bet would be to dump Bill and claim she was ignorant of what he was doing.
Even doing that she loses by looking stupid.
There is no downside to the truth other than looking mean and I am not sure that is a downside
I think Trump should put Kathleen Willey front and center in every public appearance. Sit next to her. Invite her to be at the debates. Have her on the stage behind when he speaks.