Federal law requires a judge to step away from a case in which her impartiality “might reasonably be questioned.”

Last week was a bad one for Donald Trump. The former President was indicted on thirty-seven felony counts over his handling of classified documents and what federal prosecutors say was a scheme to obstruct justice to keep those documents. But Trump did receive one bit of happy news: the case, which the Department of Justice will prosecute in Florida, is scheduled to be overseen by Judge Aileen M. Cannon, who was appointed by Trump himself, in 2020.

Last year, Judge Cannon, who serves in the Southern District of Florida, ordered a so-called special master to review the classified documents at issue, which federal authorities had found at Mar-a-Lago, and she blocked authorities from using the documents in their investigation while the review was under way. That decision was reversed several months later by a three-judge panel on a federal appellate court, which included two other Trump-appointed judges. The panel was highly critical of Judge Cannon, and called out what many perceived to be her clear bias toward the former President, writing, “To create a special exception here would defy our nation’s foundational principle that our law applies ‘to all, without regard to numbers, wealth or rank.’ ”

I recently spoke by phone with Stephen Gillers, a professor emeritus at N.Y.U. Law and an expert on judicial matters. I wanted to ask him why Cannon was assigned to the case, what steps the government might take to get her removed, and how much she could affect the trial proceedings. Our conversation, edited for length and clarity, is below.

What do we know about why Judge Cannon was given this case?

The Southern District of Florida is quite insistent in its internal rules to insure that all case assignments are done randomly. They are emphatic about the importance of random assignments, and stress that the clerk of the court where the assignments emanate from is only a functionary, who has no discretion whatsoever.

There are fifteen active judges and eleven senior judges in the Southern District of Florida. The chief judge is entitled to a reduced burden of cases. And senior judges, because many, if not all, have opted for a lower caseload or have opted not to be assigned certain categories of cases, have a lower chance of getting assigned a particular case.

So it was unlikely but not impossible.

Someone has to win the lottery, right? [On Saturday, just after we spoke, the Southern District confirmed to the Times that Cannon was randomly chosen, stating, “Normal procedures were followed.” Because the judge was chosen based, in part, on proximity to West Palm Beach, Cannon was one of seven active judges and three senior judges in the pool for the random draw.]

I have read that sometimes cases are given to judges who worked on a particular case earlier on, and Judge Cannon was involved with the documents earlier on. Is that a rule? Does it happen in some jurisdictions more than others? How does that function?

So different districts deal with this in different ways. The Southern District of Florida deals with it in a very restrictive way. It is difficult to get a case assigned to a judge merely because of another case the judge has had or has now.

And what the Southern District of Florida says—and here, I’m paraphrasing with an example—is that, if a new case comes in and is assigned to Judge A, but Judge B is already handling a case coming out of the same factual circumstance, Judge A and Judge B should get together and decide whether the new case should go to Judge B or whether Judge B’s current case should go to Judge A for the sake of efficiency. There has to be some common denominator between the cases.

But that rule says that the earlier case has to be then pending. And what Judge Cannon worked on last fall is over; it’s been over since December, when the Eleventh Circuit ruled it over. So there’s no then-pending case that Judge Cannon’s working on. If there were a then-pending case, and this case were assigned to a different judge, then that judge and Judge Cannon would get together and figure out who takes which.

It’s just not clear to a layperson why it’s not considered the same case, because it was about Trump, it was about the documents, it was about the D.O.J.’s investigation into Trump—which ended up resulting in this indictment.

The Eleventh Circuit reversed Judge Cannon’s decisions and told her to dismiss the case, which she did. It was a lawsuit Trump filed. There’s no case.

O.K. Going forward, what can the government do if it feels like a judge will not give it a fair shake?

It raises the question of recusal. There’s a statute dealing with federal judge recusal—it’s 28 U.S.C. § 455, and you should look at paragraph A. It’s the very first sentence, and that’s the most frequently cited sentence in motions to recuse. It says that a judge should recuse if the judge’s impartiality “might reasonably be questioned.”

Now, the fact that a judge’s impartiality might reasonably be questioned doesn’t mean that the judge is partial. The public may simply not trust the impartiality of the judge. Because public trust in the work of the court is a value as important as the work itself, the rule says that the judge should not sit when we can’t fairly ask the public to trust what the judge does. That rule is especially important in this case. One thing the prosecution can do is move to recuse Judge Cannon on the ground that, in light of her experience in the search-warrant case last year, her impartiality might reasonably be questioned.

And who would make that judgment if the government does push for this recusal?

The judge herself gets to make that decision in our system. If she denies the recusal, the government could go to the Eleventh Circuit and ask it to order her to recuse herself, and that’s a process called mandamus. Technically, it’s not an appeal. In effect, you’re suing the judge to force the judge to recuse. Mandamus efforts are rarely successful.

There’s one other thing the government can do, aside from doing nothing, and that is to write a letter to the judge suggesting the reasons she should consider recusing herself without being formally asked to do so. That’s done also, so as not to create a formal motion.

Who on the Eleventh Circuit would make the decision if the government goes that far?

It would be a panel of three judges. The decision they would make is whether her decision not to recuse is an abuse of discretion. That would be the question for the court. For example, one of the most remarkable mandamus decisions came in the Oklahoma City bombing case, when the Tenth Circuit Court removed the trial judge assigned to the case, because some of his personal belongings were destroyed or harmed in the bombing.

That was very unusual, but not every recusal decision has to come out the same way. One factor to consider in deciding whether recusal is necessary is how important the case is to the public and to the need for public trust. If the Eleventh Circuit panel were to reverse Cannon’s recusal decision, one thing they might say is “We are not questioning the probity or the fairness or the competence of the judge, but we don’t think we can ask the public to accept her rulings.”

So, if the government decides that it’s not going to get a fair shake from Cannon based on its previous experience with her, we will end up with this three-judge panel.

It’s impossible to say. Here, the questions are: Will they initially just write a letter suggesting that she recuse? If she does, that’s the end of it. If she doesn’t, will they make a formal motion to recuse? If she grants it, that’s the end of it. If she doesn’t, then they have to decide whether to seek mandamus. If they do, then the three judges, who are randomly chosen and who hear that mandamus petition, will have to decide whether she should be removed. If they decide that she should not, that’s the end of it. If they decide that she should, then there’ll be a reassignment.

There’s a second judge who’s assigned to this case, too—a magistrate judge. What is the role of that judge?

You can think of the magistrate judge as a judge’s helper. Magistrate judges are not what are called Article III judges. They’re not appointed pursuant to Article III of the Constitution, which creates the federal judiciary. Rather, they’re appointed by the judges of the district, who choose persons to help them in the administration of the business of the court. And they’re not appointed for life, as district judges are. They’re appointed for a term. And then they can be reappointed. But the magistrate judge is subject to the oversight of the district judge.

I want to talk generically now, because I don’t want to get into speculation and I don’t want to criticize Cannon for things she hasn’t done. But what is in a judge’s power in a criminal trial? And what are some of the ways that a judge could make a case difficult?

Let me just back up a second. What’s a trial? A trial is a competition between two sides over which story is true, right? That’s what we’re talking about. The prosecution has a story, the defense has a story, and the jury is going to decide whom to believe. They make that decision based on information that the judge, applying the rules of evidence, allows the jury to hear. The judge’s great power here is to admit or exclude evidence—and the judge’s discretion in that realm is broad. A judge can affect the result of a trial by refusing to allow either side, more often the prosecution, to introduce or to argue certain evidence to the jury.

For example, in this case, a lot of the evidence, as we can glean from the indictment, will come from people, including lawyers, who heard Trump say something. So, right there, you have what’s called the hearsay problem. This is going to be critical to the prosecution’s case. What a trial judge here can do is decide whether the hearsay rule forbids the introduction of particular evidence. It’s a complicated rule. And so, to answer your question in the first instance, the judge, by allowing or refusing to allow information to go to the jury, can hinder the ability of either side to tell the story it wants to tell.

There’s one more thing you must know, and that is that, after the prosecution rests, and then again after the defense rests but before the case goes to the jury, the defense can make a motion for a directed verdict for acquittal. What that says in effect is: “Judge, the evidence of guilt is so flimsy that it cannot amount to guilt beyond a reasonable doubt. Therefore, there’s no need to send this case to the jury. You should just throw it out, because as a matter of law they have not established guilt beyond a reasonable doubt.” If the judge grants a directed verdict of acquittal before the case goes to the jury, that’s the end of it. That cannot be appealed.

And, even after the jury comes back with a verdict or a sentence, the judge can change that, too, right?

Yes. After the verdict, the judge could say, “I think the jury got it wrong. I’m going to direct a verdict of acquittal, despite the jury’s verdict of guilt.” But the prosecution can appeal that to the circuit court.

But you’re saying that, if the judge were to do it at an earlier step, before the jury reaches a verdict, there’s no appeal.

Then the case is over, the defendant walks away, and there’s no review.

Trump has an incentive to drag this case out, and the government has an incentive to get it done quickly to avoid the heart of a Presidential-election cycle. I would imagine that a judge can also affect the speed of a trial, right?

Yes. There could be motions that a judge takes her time deciding. A judge could affect the length of the trial by allowing witnesses who another judge would say should not testify, because they’re duplicative or because what they want to say is irrelevant. A judge can certainly affect the time the trial begins, and, yes, he or she can affect when the trial ends. The speedy-trial rule requires that the trial begin before a certain duration of time has passed after the indictment. But that rule has a lot of exceptions, and the judge can extend that time.

Is there some advantage for the government to wait and see how the trial is going before it pushes for a recusal? Would it have a stronger case for recusal that way?

If there is a basis to move to recuse, you can’t wait around. You have to do it quickly. You can’t wait around to see whether the judge rules on motions in your favor.

Are there downsides to going for recusal right away?

The problem with going for recusal right off the bat is that you may lose in the circuit, and now you’re trying a case before a judge you’ve accused of being unable to appear impartial—and that’s not pleasant. So the government may decide that it’s just better to make the strongest case they can and hope that she behaves like a judge.

Given what we saw regarding Cannon’s behavior during the previous case, do you think that the government will or should go for a recusal?

Given the importance of this case, perhaps the most important criminal trial in the history of the United States—certainly the most watched—and in light of what Judge Cannon did in the search-and-seizure case last year, I think she must step aside. I think she must grant a motion to recuse herself, unless she does it before a motion is even made.

And the reason I say that is that she treated Trump as special, or, to put it another way, she was partial to Trump as a former President, which should not have any influence on the way this trial is conducted. I’m concerned that the partiality she expressed in her decisions last year creates a reasonable perception in the mind of a fair-minded person that she is not impartial—which is the test. Her behavior when she was ruling on the search-and-seizure case creates a reason to doubt her impartiality.

But when you say “must,” you mean from an ethical sense.

No, “must” in a rule sense. There’s a rule.

O.K., but there’s also no way to enforce the rule, right?

Except through mandamus.

That suggests to me that you think the government should or will go to mandamus.

What it means is that I think, if the government does so, she must grant the recusal, and if she doesn’t the Eleventh Circuit must order it. It’s a different kind of question to ask whether I think the government should make the motion, because the government may assess the chances differently than I do. If the government agrees with me that she must recuse because of the tender way she treated Trump in her rulings last year, then I think it must make that motion. But it may not agree with me.