Special prosecutors, investigators, and counsels are usually a bad idea. They are admissions that constitutionally mandated institutions dont work and can be rescued only by supposed superhuman moralists, who are without the innate biases inherent in human nature.
The record from Lawrence Walsh to Ken Starr to Patrick Fitzgerald suggests otherwise. Originally narrow mandates inevitably expand on the cynical theory that everyone has something embarrassing to hide. Promised short timelines and limited budgets are quickly forgotten. Prosecutors search for ever new crimes to justify the expense and public expectations of the special-counsel appointment.
Soon the investigators need to be investigated for their own conflicts of interest, as if we need special-special or really, really special prosecutors. Special investigations often quickly turn Soviet, in the sense of Show me the man and Ill find you the crime."
The investigation is venturing well beyond the original mandate of rooting out evidence of Russian collusion. Indeed, the word collusion is now rarely invoked at all. It has given way to its successor, obstruction. The latter likely will soon beget yet another catchphrase to justify the next iteration of the investigations.