Let’s say, however, that Trump receives a subpoena and fights it to the Supreme Court. And let’s say that, in the end, the Court sides with the special counsel and tells Trump he has to appear before the grand jury.

What if the president just says “no”?

If a normal citizen were to do that—to refuse to testify in response to a legitimate order—the answer would be relatively easy: The prosecutor would go to court, show the judge the valid subpoena and the refusal, and ask the judge to find the person in contempt of court.

There are, notably, two flavors of contempt of court: civil and criminal. Civil contempt is nothing more, nor less, than an effort to compel a witness to appear as ordered. Typically, a witness who defies a subpoena is arrested on a civil-contempt citation and put in jail. They then remain there until they change their mind and testify, or until the investigation ends and the grand jury that summoned them shuts down. Either way, whether they change their mind—what’s called “purging yourself” of contempt—or whether the investigation concludes, the term of imprisonment is time-limited. Indeed, the person in contempt, sometimes called a contemnor, actually holds the keys to their prison.

By contrast, criminal contempt is a separate criminal offense, and the process for proving it is much like that of any other crime. The prosecutor can decide to charge the contemnor with the criminal charge of contempt and try to prove the case in court beyond a reasonable doubt. If convicted, the defendant can be sentenced to a term of years and doesn’t have a key to his or her jail cell.

The case of Susan McDougal is a good illustration of the difference between the two types of contempt. She was a business partner of Bill and Hillary Clinton who was convicted of real-estate fraud in 1996. After McDougal went to jail, Starr called her to testify before a grand jury, and she refused to do so.

McDougal then languished in jail for about two years while the grand jury continued its work. After the grand jury finished its term without ever hearing from McDougal, Starr brought a criminal prosecution against her for contempt. After a trial, McDougal was acquitted and, since that time, has been an advocate for reform of the contempt system (and a critic of the Starr investigation, too). But whether just or unjust, McDougal’s is the typical case: Refuse a lawful order to testify and you go to jail.

A president refusing an order would be uncharted territory.

Presumably, the court that issued the subpoena would find the president in civil contempt, just as it would any other citizen. But after that … that’s where it gets interesting.

An ordinary American would go to jail. Some contemnors voluntarily show up for incarceration because they are trying to make a point; for example, that’s the typical practice for a news reporter who goes to jail to protect a source.