We may have crossed the Rubicon on that
They may be able to stop Mueller, but they will have a price to pay if they try. The outcome of that conflict cannot be predicted. A large portion of the GOP has held on to the illusion of their impartiality by backing any future Mueller findings as legitimate. If they simply refuse to even consider them, we will all know exactly who they are and where they stand.
They're not going to be able Graham or Kennedy their way out of that one.