The easiest way for the Russians to diminish the potency of this dossier would be to deliberately insert disinformation into it. The upshot was that a bunch of “facts” would find their way into the dossier which, over time, could be disproved. This would then enable the Russians and, not incidentally, Trump himself to claim that everything in the dossier was false, even if something in it turned out to be true. They and all of their mouthpieces could then point at it and scream, “FAKE NEWS!” And they wouldn’t be wrong.
