As President Trump and Special Counsel Robert Mueller continue to dance around the possibility of an interview, it is, perhaps, useful to think about how a confrontation between the two might play out. Imagine that negotiations come to an unsuccessful conclusion and Mueller is motivated to issue a subpoena to Trump.

What happens then?

As far as the public record reflects, a president has only been subpoenaed once before, when Independent Counsel Kenneth Starr tried to compel former President Bill Clinton to appear in front of a grand jury during his sprawling inquiry into the Clintons in the 1990s, an investigation in which I served as a senior counsel. In the end, Clinton agreed to a voluntary interview and the subpoena was withdrawn, so the country never learned what could happen if a president were to fight a subpoena.

President Trump might very well have good grounds for attempting to avoid an appearance. As far back as the 1807 federal case against Aaron Burr for treason, then-President Thomas Jefferson objected to a subpoena, and the court there opined that it would be problematic for the judiciary to order a president to be in a particular place at a particular time. Much the same language was used by the Supreme Court when it weighed in on Paula Jones’s suit against Clinton alleging sexual harassment: The suit could go forward, but courts should be cautious about ordering presidents around.

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.

But for contemnors who don’t show up voluntarily, the court sends the U.S. Marshals Service out to arrest them and bring them to jail in handcuffs. It’s not a pleasant experience, but it’s common enough—arrest warrants are executed every day around the country.

However, that’s just not going to happen to a president who refuses to testify. A president who declines to appear before a grand jury certainly isn’t going to voluntarily show up for prison. The court issuing the subpoena would then have to decide to send Marshals after the president. And if the Marshals arrive at the president’s location to arrest him, the only thing likely to happen is that they would get in a gunfight with the Secret Service.

I am, of course, not really serious about the gunfight—but if the president does not want to appear, there simply is no realistic way for the court to physically force him to do so. Thus, the civil-contempt route seems unavailing. The idea of criminal contempt as an enforcement mechanism is likewise of little utility: As I’ve written before, a long-standing legal opinion within the Department of Justice says a sitting president cannot be indicted for criminal conduct. Mueller would almost certainly follow that guidance.

Absent a legal mechanism to compel the president’s testimony, there’s really only one question left to ask: How would the political system react to such a refusal? It is likely that many would call the president’s refusal to obey a court’s lawful order a “constitutional crisis,” and that’s probably accurate. But it’s a crisis for which the country is wholly unprepared. Would it result in impeachment? Would the citizens of the United States call on their representatives to act? Would they act? Would the president pay a price at the ballot box?

These are uncomfortable questions. Americans like to think that the rule of law is paramount in this country, and for the most part it is. Compliance with legal requirements is as strong a behavioral norm there is in the American political landscape; history is littered with figures who defied the law and lost their positions of influence. But saying “thus it has been in the past” is not the same thing as saying “and thus it will always be in the future.”