We need to flush out the source(s). The best form of attack is to insist that the source is Rather's daughter, and that is why he is stonewalling. Rather will then switch into defense of his daughter mode, and rat out the source(s).
Background: Ben Barnes (who was part of the interview) knows Rather's daughter very well.
And he did fund raisers for her and her Democratic Party cronies so it's highly likely he'd take fake documents to help her.
I hear you!