Leave aside for the moment the pesky detail that such claims are fundamentally inconsistent with the Constitution and the idea that no person is above the law. The claim that the president is immune from the criminal process also winds up being potentially bad for Mr. Trump. It may mean he would lack the right to refuse to testify — because he could not incriminate himself given his supposed constitutional immunity.

The mishmash of bad constitutional arguments being floated by Mr. Trump has to cause Mr. Mueller concern. And that is why Mr. Giuliani’s story that Mr. Mueller’s team told him that Mr. Trump cannot be indicted seems at best incomplete. It is true that the special counsel regulations (which I drafted in 1999 for the Justice Department) generally require the special counsel to obey Justice Department policy. And it is also true that Justice Department policy is that a sitting president cannot be indicted. But the regulations contemplate that a special counsel could, in appropriate circumstances, depart from Justice Department policy.

The regulations had to be written that way. Those of us who created them could not foresee all the possible permutations of law and facts that would unfold in the years to come. If congressional leadership, for example, was in criminal cahoots with the president, no one would want the special counsel to be powerless to indict or to report information to the full Congress for impeachment.

Accordingly, the regulations permitted the special counsel to seek a departure from Justice Department policy, by going to the acting attorney general (in this case, Rod Rosenstein) and requesting it. The idea was that if responsibility for decision-making was vested in Justice Department leadership, decisions to protect the rule of law were more likely to be made. And as a safeguard against wrongdoing by Justice Department leadership, the regulations require transparency in the process: If the acting attorney general refuses a special counsel request, he must notify the majority and minority parties in Congress.

In this way, the regulations put a thumb on the scale in favor of having Mr. Mueller seek an indictment if he finds evidence of criminal wrongdoing by Mr. Trump. Unlike the Independent Counsel Act, a predecessor to the special counsel regulations that required the prosecutor to write a detailed final report to Congress, the regulations require only a substantive report when the acting attorney general overrules the special counsel. The acting attorney general is free to write one otherwise, but the only way Mr. Mueller can ensure such a report is written is to make a request that is overruled.

All of this explains why Mr. Giuliani’s story that Mr. Mueller has concluded he cannot indict a sitting president seems implausible and incomplete. It is far more likely that Mr. Mueller has concluded that Justice Department policy currently forbids such a step, but that he has a path forward toward seeking indictment if he believes it warranted. And Mr. Trump, whose Justice Department has, with his blessing, repeatedly overruled longstanding Justice Department positions at an unheard-of rate, is in no position to complain if Mr. Rosenstein overrules these two old opinions. Of course, if Mr. Rosenstein refuses to overrule them, he would still be creating a record that Congress may use as it considers impeachment.

Thus the various pieces of the constitutional and regulatory scheme work together: If indictment is off the table, then impeachment must be on it; and (perhaps in a future setting) if impeachment is off the table because of nefarious congressional activity, then indictment must be on it. That is the genius of our system, and the only way to ensure we remain a government of laws which no one is above.