The verifiable portions of the dossier have been proven to be factual. None of it has been proven to be false. It is a collection of intel pieces, it was never intended to be a court document that needs to be 100% correct. It is a collection of data points, most are right, some are bound to be wrong--thus far it is batting 1.000
FISA warrants were obtained on Manafort and Flynn and the 2 Russian banks. Contents of the warrant have not been made public but when they do, I highly suspect they will contain audible phone calls with Trump which will become the smoking gun evidence to the American public (akin to Nixon's voice on his tapes)
Repubs are trying to undermine the dossier and thereby claim they should not have been used to obtain the FISA warrants, inadmissible evidence. They are playing a long game in the court of public opinion. It will be in Congressional hearings at which time the warrant's tapes will be played. It was public opinion is what forced Congress to act against Nixon.
If I were still a Repub (thank goodness I am not), I would be VERY concerned about the later portion of 2018. If they don't get rid of Trump by July 4 their ship is going to totally implode.