Therefore, Rosenstein’s flouting of the regulations means Mueller’s investigation is a fishing expedition. It is already straying far afield from suspicions about Trump collusion in Russia’s election-meddling — which, we need to remind ourselves, is the purported rationale for the probe, and thus for Mueller. The probe’s focus has morphed from collusion to obstruction: the chief-executive’s weighing in on Flynn’s prosecution, pushing for disclosure of true information that he was not a suspect in the Russia investigation, and firing of the FBI director — all actions Trump was constitutionally entitled to take.

Mueller has also broadened his scope to include the scrutinizing of financial activities of Trump associates, reportedly based on hunches about possible bribery and money-laundering. These, in turn, are based on the assumption that there was collusion — notwithstanding that months of investigation by the FBI and several congressional committees has turned up no such evidence.

In addition, there are conflicts of interest that are apt to discredit the investigation, regardless of whether they technically require disqualification. Rosenstein selected Mueller despite the latter’s close friendship and professional ties to Comey. Now that obstruction is suddenly the focal point of the probe, Comey is clearly a central witness. Meanwhile, no doubt relying on Mueller’s sterling reputation, Rosenstein gave the special counsel free rein on staffing. Mueller promptly made tin-eared hires: lawyers who, despite their impressive prosecutorial credentials, are Obama and Clinton donors. One of them, Andrew Weissmann, is also plagued by the scorched-earth reputation he developed as special prosecutor in the Enron investigation, particularly the infamous prosecution that destroyed the Arthur Andersen accounting firm — which Weissmann indicted on very thin proof for, yes, obstruction of justice . . . only to have the conviction thrown out by the Supreme Court.