Special Counsel Robert Mueller’s final report is predicated, as far as we know, on a potentially explosive assumption.

Consider a head scratching set of conclusions. The Special Counsel wrote that “the evidence does not establish that the President was involved in an underlying crime related to Russian election interference,” and, in the words of Attorney General Bill Barr, “the report sets out evidence on both sides of the question” of whether the President committed the crime of obstruction. The Attorney General stated, in testimony before Congress on Tuesday, “it was important for people to know the bottom line conclusions of the report,” and “from a prosecutor’s standpoint the bottom line is binary, which is charges or no charges.”

Why are those conclusions so curious?

It’s extraordinary that the Special Counsel prosecutors and the Justice Department were even contemplating whether a sitting president was guilty of a crime. According to currently binding opinions of the Justice Department’s Office of Legal Counsel (OLC), a sitting president cannot be indicted, let alone prosecuted. So it is difficult to know how the Special Counsel’s report landed on any assessment of whether the President himself had committed a crime.

Over the past two years, some close observers had even doubted whether the Special Counsel was investigating whether the president was guilty of criminal obstruction; the alternate theory was that Mueller was investigating Trump’s interference in the Russia investigation as a potential “abuse of power” subject not to criminal law but to potential impeachment.

So, lo’ and behold, Mueller appears to have looked directly into the question whether “the President was involved in an underlying crime.” And Barr now suggests the final report’s conclusions involved prosecutors’ familiar binary decision of “charges or no charges.” In other words, Mueller was apparently somehow able to reach these standard questions despite the President’s anything-but-standard immunity from indictment.

That should worry the White House to no end. That’s because back in Manhattan, the Southern District of New York appears to have significant evidence that President Trump may have been involved in a criminal conspiracy to make hush money payments in violation of federal campaign finance laws, and the scheme for making those payments may have involved federal tax and other financial crimes.

Trump should worry that the Southern District of New York could, at a minimum, walk through the same open door as Mueller and reach the same question–a formal determination assessing if the President committed a crime. Whether in the form of a prosecution memo, or a memo reviewing the evidence, there would be an interest in preserving the analysis even if an indictment could not be brought presently because Trump is President. But that’s the kind of outcome the OLC’’s Opinion in 2000 seemed designed to avoid. It concluded that indictment was foreclosed due to “the disabilities that stem from the stigma and opprobrium associated with a criminal charge, undermining the President’s leadership and efficacy both here and abroad.” And the Opinion concluded that even a sealed indictment was not permitted, because it could leak. “Given the indictment’s target it would be very difficult to preserve its secrecy,” the opinion stated. The same holds true for a formal determination by prosecutors of the President’s criminal guilt.

For a sitting President there may be little practical difference between an indictment, with trial awaiting until he or she leaves office, and a formal conclusion that the president could be indicted.

At bottom, this convergence of events exposes a potential tension with the OLC opinions’ holding that a sitting President is immune from indictment and the practical work of the Justice Department. As I have written before in a related context, “It can’t be that Mueller has the authority and publicly understood duty to investigate Trump for potential crimes, but not the power to say whether Trump was involved in any offences.” Perhaps Mueller thus decided the door was open to him because of the extraordinary nature of his mandate under the special counsel regulations which were, indeed, contemplated and designed for the investigation of a President. But the issue is broader than just the case of the special counsel.

The Justice Department can hold to a position of not indicting a sitting President, but once the Department is assessing the criminal liability of actors around the President, it can’t easily avoid assessing the President himself; and once prosecutors know that there is sufficient evidence of a crime by Individual-1, how can that be ignored? We may have thus found not just a flaw in the OLC position, but also its limits. Mueller’s investigation appears to be an object lesson that the OLC position should not be read to preclude investigation of a sitting President and potential reporting about prosecutorial conclusions in that investigation.

We should soon know some answers and bring this head scratching to an end.

The eventual release of the Mueller report may be a signal not only to prosecutors in the Southern District but also to the public. It is likely to raise the public’s expectation that federal prosecutors may well be able to state whether they conclude the President committed a crime.