Deputy Attorney General Rod J. Rosenstein on his way to the Justice Department on Tuesday. He'll meet with President Trump on Thursday. (Chip Somodevilla/Getty Images)
Neal Katyal  is the former acting solicitor general of the United States and presently serves as a partner at Hogan Lovells and the Saunders professor of national security law at Georgetown University.

Thursday’s meeting between Deputy Attorney General Rod J. Rosenstein and President Trump carries the highest of stakes: Besides special counsel Robert S. Mueller III, Rosenstein is the most important person involved in the investigation of the Trump administration’s possible ties to Russian interference in the 2016 election. That is by design. The special counsel regulations, which I had the privilege of drafting in 1999, make Rosenstein what corporate mavens call a “key man.” If Rosenstein is removed, Trump could very easily cripple the investigation.

The president knows it. Trump’s attorney, Jay Sekulow, this week called for Solicitor General Noel Francisco, who would probably replace Rosenstein in overseeing Mueller’s work if Rosenstein leaves office, to “pause” the investigation and to take “a step back.”

Which is why Rosenstein should prepare for Thursday by sending Congress, through appropriate channels, a description of the evidence of wrongdoing Mueller has already turned up. There’s no way to know what a meeting with the volatile president might bring. And the search for the truth might depend on what steps Rosenstein takes beforehand.

Remember what the special counsel regulations are all about. Our Constitution puts the executive branch in control of prosecutions. That includes all prosecutions, including those of the president himself. The executive acts as the guardian for criminal prosecutions, a design choice that tees up the Platonic question of who will guard the guardians. The special counsel regulations are designed to provide for an independent prosecutor, albeit one who must still ultimately be supervised by the executive branch. The regulations make the attorney general (or, in cases such as the Russia probe in which the attorney general is recused, the deputy attorney general) the supervisor of the investigation. The attorney general and the deputy are the president’s people — he nominated them, and they are part of his executive branch. But they are not the president himself, obviously, and they work in the Justice Department, not the White House.

The balance struck was delicate. A special counsel such as Mueller would have “day-to-day” independence, but the attorney general could shut down any “investigative or prosecutorial step.” That is part of our constitutional design — there was not an appropriate way to totally remove the attorney general from the proceedings. Instead, the best that could be done was to structure the arrangement so that someone like Mueller would have general daily freedom to do what he wanted, but that someone such as Rosenstein could stop him if warranted.

Obviously, we wrote the regulations with the fear that one day an attorney general could be more loyal to the president who appointed him than to the rule of law. So we made it hard for the attorney general to stop a special counsel. We set a high threshold for refusing a special counsel determination: It had to be “so inappropriate or unwarranted under established Departmental practices that it should not be pursued.” And we required the attorney general to notify Congress — both the majority and minority — if he ever said “no” to a special counsel. By shining a light on the internal actions of the Justice Department, we hoped to incentivize good government.

Rosenstein appears to have done exactly what the regulations contemplate. He has let the Mueller investigation unfold, and the consequences have been dramatic. The president’s former national security adviser has pleaded guilty to a felony. The former head of his campaign has been convicted by a jury of financial fraud, pleaded guilty to additional charges and will cooperate with Mueller. Twenty-five Russians have been indicted on a charge of attempting to influence the election. The list of achievements is long. All of that has been possible because Rosenstein took the step of naming Mueller as special counsel, and it looks as though Rosenstein has protected the investigation ever since.

But we cannot know for sure. That is because the special counsel regulations require the attorney general to report only at the close of the investigation to Congress about any times he said “no” to a special counsel. We wrote them that way on purpose: Interim reports of ongoing cases are generally bad practice, threatening both the investigation and the reputations of individuals without due process. But the downside is that now no one outside the Justice Department has great insight into what Rosenstein has been doing; the public can only infer things from external signs, such as the number of indictments and pleas. In 1999, we anticipated that interim reports to Congress could be made on an as-needed basis, but there is no requirement for them, and it’s not clear that Rosenstein has made any (they can be kept secret).

What is true for Rosenstein would be true of Rosenstein’s replacement, too. The new acting attorney general for purposes of the Russia probe could say “no” to Mueller for years, and no one else would know until the investigation closed. And while we did set a very high legal threshold for interference with a special counsel investigation, the Trump administration has repeatedly shown comfort playing fast and loose with legal rules. In the end, the special counsel regulations are nothing more than what James Madison called a “parchment barrier” — just a piece of paper, dependent on the spirit of the person enforcing it. There are all sorts of ways a Trumpist replacement for Rosenstein could stymie an investigation, ranging from dramatic (firing Mueller outright) to low-key (refusing to provide Congress with any interim reports and simply dragging the investigation out endlessly, without any updates to the public) or even more subtle (starving the budget or depriving Mueller of key personnel).

So what to do about it?

One option is to pressure Trump to be a little more like Richard Nixon. While Nixonian tendencies ordinarily seem to come pretty spontaneously for the president, Trump here has pointedly not made the same promise that Nixon did in 1974, which is that he and the acting attorney general would not remove the special counsel without the express agreement of both the majority and minority in Congress. As former Whitewater special prosecutor Kenneth Starr and I argued earlier this year, “If President Trump cannot agree to an investigation modeled on what Richard Nixon agreed to, the question will linger: Just what is he afraid of?”

Another option is for Congress to consider passing legislation to protect Mueller and the independence of his investigation. Such legislation has been pending almost as long as the investigation has, and unfortunately, so far, it looks likely to remain in limbo.

But the final choice is for Rosenstein himself. The special counsel regulations did contemplate interim reports to Congress in certain circumstances. Nothing in the regulations forbids them, and while there are possible restrictions on grand jury material and the like, there is much information that could be provided. Rosenstein could, right now, tell Congress (or even a small group of members, with appropriate safeguards, including secrecy) what has happened — what Mueller has learned so far, whether Rosenstein has ever said “no” to Mueller and where the investigation is headed now.

Such a move would be unusual, to say the least. But it is a way for Rosenstein to safeguard his legacy. And it could also safeguard the very principle that no one is above the law. Not even the president — and not even this president.

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Sitting presidents can’t be prosecuted. Probably.