Deputy Attorney General Rod Rosenstein should recuse himself from the probe into the Trump campaign’s ties to Russia and the President’s apparent attempt to obstruct the FBI’s inquiry. Rosenstein himself played a key role in the events at the center of the controversy, and his continued involvement casts a shadow over the ongoing investigation.

So far, the core of the case against President Trump is as follows: The President pressured FBI Director James Comey to end the Bureau’s inquiry into links between the Russian government and Trump’s top advisers. When Comey refused, the President fired the FBI chief and claimed he had acted based on the “clear recommendations” of Rosenstein and Attorney General Jeff Sessions. Sessions, for his part, said that his recommendation was based on “the reasons expressed by the Deputy Attorney General in the attached memorandum.” That three-page memorandum from Rosenstein faulted the FBI head’s handling of the probe into Hillary Clinton’s e-mails.

Put more bluntly: The allegation is that President Trump fired Comey to impede the Russia investigation and then tried to passed it off on Rosenstein.

The Justice Department’s recusal regulation, 28 CFR 45.2, states that “no employee shall participate in a criminal investigation or prosecution if he has a personal or political relationship with . . . [a]ny person or organization substantially involved in the conduct that is the subject of the investigation or prosecution.” It goes without saying that no Justice Department employee should participate in a criminal investigation if he is himself a person substantially involved in the conduct that is the subject of the investigation. The subject of the investigation (or at least, one significant subject) is whether Trump fired Comey to obstruct justice and then tried to cover it up by enlisting Rosenstein. How is Rosenstein not a person substantially involved in that?

One can argue over whether Rosenstein, as an officer of the Justice Department, counts as an “employee” subject to the Department’s recusal rule. Attorney General Sessions did not rest on this distinction in March when he recused himself from the Russia probe. The Justice Department’s recusal rule reflects the fundamental principle that nemo iudex in causa sua: no man should be the judge (or the prosecutor) in his own case. Whether or not 28 CFR 45.2 applies to Rosenstein, the underlying principle certainly does.

Has Rosenstein done enough to remove himself from the obstruction of justice investigation by appointing former FBI Director Robert Mueller as special counsel? Flatly, no. While Mueller does have jurisdiction to investigate allegations that President Trump tried to obstruct the FBI’s Russia probe, Mueller remains under Rosenstein’s thumb. Rosenstein, acting as Attorney General following Sessions’s recusal, has control over Mueller’s budget and can decide at the start of any federal fiscal year (the beginning of October) to shut down Mueller’s investigation (see 28 CFR 600.8(a)). So too, Mueller must inform Rosenstein at least 72 hours in advance of any “major development” in the investigation, which includes not only the filing of criminal charges or the arrest of a defendant, but also the execution of a search warrant or an interview with a significant witness “when the events are likely to receive national media coverage” — which here, they surely are (see 28 CFR 600.8(b) and U.S. Attorneys’ Manual 1.13.000). And Rosenstein has the power to order Mueller not to pursue any investigative or prosecutorial step (see 28 CFR 600.7). This is far too much power for someone so close to the center of an investigation to wield over its direction.

There is nothing to the argument that Attorney General Sessions’s recusal renders Rosenstein’s continued involvement in the investigation essential. Under the Justice Department’s recently revised order of succession, Acting Associate Attorney General Jesse Panuccio would stand in Rosenstein’s stead, and if Panuccio were for some reason unable to fill Rosenstein’s shoes, then the U.S. Attorney for the Eastern District of Virginia, Dana Boente, would be the next in line. [Update: The Senate confirmed Rachel Brand as Associate Attorney General at the end of last week. Brand, not Panuccio, will now follow Rosenstein in the order of succession. h/t Josh Blackman] There exists a clear protocol for how to proceed in the event of a double recusal at the top of the chain. All that stands in the way is Rosenstein’s refusal to remove himself from the matter.

Before joining the Trump administration, Rosenstein had a well-earned reputation for being a conscientious and honorable public servant. Based on that reputation, we might hope Rosenstein would not interfere with the special counsel investigation. But based on that same reputation, we might expect Rosenstein to have recused himself already. If he doesn’t, he will place his credibility into even greater jeopardy.