Donald Trump's 5 reasons to fire Rod Rosenstein reveal true aim: Obstructing Robert Mueller Donald Trump has floated 5 reasons to fire Rod Rosenstein and all fall apart under scrutiny. His true aim is clear: obstructing Robert Mueller's Russia investigation.

Norman Eisen and Richard Painter | Opinion contributors

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President Trump reportedly is considering firing Rod Rosenstein, the deputy attorney general who appointed special counsel Robert Mueller and supervises his investigation into Russian interference in the 2016 election. To prepare the way, Trump has by our count floated five rationales internally and externally for doing so. The briefest scrutiny of these purported justifications shows that they are baseless, and makes apparent the president’s true motivation: to obstruct the investigation that Rosenstein oversees.

Trump has reportedly complained about Rosenstein being a Democrat and coming from heavily Democratic Baltimore. In fact, Rosenstein is a decades-long registered Republican who worked as a federal prosecutor in Baltimore. That was part of a long career at the Justice Department devoted to the rule of law under both Republican and Democratic presidents. He was selected from a pool of Republican lawyers and nominated by Trump for his position as deputy attorney general.

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Trump has also suggested that Rosenstein acted improperly when he reauthorized the Justice Department’s application for a Foreign Intelligence Surveillance Act court warrant to monitor onetime Trump campaign adviser Carter Page. Rep. Devin Nunes, R-Calif., attempted to paint this application as improper in his infamous memo on the topic.

But closer examination led most observers to conclude that the Justice Department had followed appropriate procedures. In any event, the warrant was first authorized long before Rosenstein arrived; he signed off on a much later application for reauthorization, in which the department successfully demonstrated to a judge that the warrant had already provided valuable information.

Additionally, Rosenstein has apparently drawn Trump’s ire by approving search warrants against Michael Cohen, Trump’s personal attorney. As one of us has written, these warrants result from an investigation of very serious allegations of criminal conduct, including possible illegal campaign contributions by Cohen. Because they target an attorney, these warrants underwent heavy review within the Justice Department, and like all warrants they were approved by a federal judge. The notion that Rosenstein acted improperly is unfounded.

Next, Trump is apparently suggesting that Rosenstein is close to former FBI director James Comey — and has appointed the special counsel and taken other steps to get revenge for his firing. This theory is as flimsy as the rest: While the two worked together, they are not friends. It is also inconsistent with other evidence, including Rosenstein's extremely harsh assessment of Comey’s work (on the Hillary Clinton email case) in a memorandum he wrote before Comey’s firing.

It is that memorandum that leads to the final main line of attack on Rosenstein. The president reportedly believes that Rosenstein has a conflict of interest because he wrote that memorandum and because Mueller is investigating the circumstances surrounding Comey’s firing. That would make him a witness, this argument goes, and so render him conflicted in supervising Mueller.

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This sally rests on a profound misunderstanding of the law of conflicts. Being a fact witness does not require a Justice Department employee to stop working on a matter immediately. None of the relevant conflicts rules requires a supervising official who is a fact witness to step away from an investigation (if there is no business or personal interest in the outcome of a case). Even if Rosenstein is a fact witness, the issue of recusal arises only when and if he is going to testify at trial.

The American Bar Association’s Model Rules of Professional Conduct state that a lawyer should not act as an advocate at a trial where the lawyer will also be a necessary witness. The ABA rules also state explicitly that a lawyer from one firm is not disqualified if another lawyer from the same firm is a witness.

The purpose of these rules is to ensure that a court or a jury is not “confused or misled by a lawyer serving as both advocate and witness.” It stretches this principle beyond the bounds of reason to suggest that this means a Justice Department lawyer cannot supervise the investigation of a case if there is even a possibility he could be a witness. If such a standard were applied in the private sector, just about every corporate general counsel would be required to resign at the outset of any investigation in which he or she could be called as a witness. That is nonsensical.

Everything we know about Rosenstein's handling of the special counsel’s investigation suggests that he has acted with integrity. He has clearly defined Mueller’s jurisdiction. When a matter that appeared to be unrelated to that jurisdiction appeared, he referred it to the appropriate U.S. Attorney's office rather than expanding the special counsel’s scope. Far from giving Mueller sprawling Ken Starr-like power to go after whatever potential offenses he comes across, Rosenstein has kept the special counsel focused on Russian interference, potential cooperation between Russia and the Trump campaign, and offenses such as obstruction of justice and financial crimes arising directly from that investigation.

Under these circumstances, if Trump fires Rosenstein, it will clearly be for one reason and one reason alone: to impede the lawful investigation of the president and those close to him. Similar actions by President Nixon in the Saturday Night Massacre led to his downfall. The firing of Rosenstein would have the same outcome for Trump.

Norman Eisen, chair of Citizens for Responsibility and Ethics in Washington, and Richard Painter, a law professor at the University of Minnesota, were chief White House ethics counsels for the Obama and Bush administrations, respectively. Follow them on Twitter: @NormEisen and @RWPUSA