I’ve been hearing that question a lot these days. News reports indicate that Special Counsel Robert Mueller may try to coerce President Trump’s testimony by issuing a grand-jury subpoena if the president does not agree to a "voluntary" interview. That has sparked a public debate over the question of whether Mueller, an inferior executive officer, has such authority to strong-arm the chief executive ‐ the official in whom the Constitution reposes all executive power, including the power that Mueller exercises only as long as the president permits it.
I don’t think he does.
To be clear, there is no question that Mueller, as a special counsel, is a federal prosecutor who has the authority to issue grand-jury subpoenas. But everyone who works in the Justice Department has a boss, including the attorney general (who answers to the president). As special counsel, Mueller answers to Deputy Attorney General Rod Rosenstein (because Attorney General Jeff Sessions recused himself from the so-called Russia investigation). That means Mueller has the authority to issue a subpoena to the president unless Rosenstein ‐ or the president ‐ tells him not to.
Before we come to whether the deputy AG should clip the special counsel’s wings, let’s address one point of confusion.
Many people believe, as I do, that the president should not be subjected to questioning by a prosecutor on the facts as we presently know them. From that premise, however, they argue that Mueller may not subpoena the president, or that the president may ignore any subpoena. Neither of those things is true.
A prosecutor has the power to subpoena virtually anyone. In our system, there are very few limits on what the grand jury may investigate. A comparison usefully illustrates this point. I’ve frequently observed that by appointing Mueller without first establishing a basis to believe a crime warranting investigation had been committed, Rosenstein violated regulations that govern special-counsel appointments. By contrast, the grand jury has no such constraints ‐ it can investigate pretty much anything. There is no proof hurdle ‐ such as "probable cause" or "reasonable suspicion" ‐ that has to be surmounted. In fact, a grand jury is free to investigate even if it just wants to satisfy itself that a crime has not been committed.