Correction: An earlier version of this op-ed misspelled the name of former defense secretary Caspar Weinberger. This version has been updated.

Laurence H. Tribe is the Carl M. Loeb University Professor and Professor of Constitutional Law at Harvard Law School. Richard Painter, a law professor at the University of Minnesota, was chief White House ethics lawyer for President George W. Bush from 2005 to 2007 and is vice-chair of Citizens for Responsibility and Ethics in Washington (CREW). Norman Eisen, a senior fellow at the Brookings Institution, was chief White House ethics lawyer for President Barack Obama from 2009 to 2011 and is chair of CREW.

Can a president pardon himself? Four days before Richard Nixon resigned, his own Justice Department’s Office of Legal Counsel opined no, citing “the fundamental rule that no one may be a judge in his own case.” We agree.

The Justice Department was right that guidance could be found in the enduring principles that no one can be both the judge and the defendant in the same matter, and that no one is above the law.

The Constitution specifically bars the president from using the pardon power to prevent his own impeachment and removal. It adds that any official removed through impeachment remains fully subject to criminal prosecution. That provision would make no sense if the president could pardon himself.

The pardon provision of the Constitution is there to enable the president to act essentially in the role of a judge of another person’s criminal case, and to intervene on behalf of the defendant when the president determines that would be equitable. For example, the president might believe the courts made the wrong decision about someone’s guilt or about sentencing; President Barack Obama felt this way about excessive sentences for low-level drug offenses. Or the president might be impressed by the defendant’s subsequent conduct and, using powers far exceeding those of a parole board, might issue a pardon or commutation of sentence.

Other equitable considerations could also weigh in favor of leniency. A president might choose to grant a pardon before prosecution of a person when the president believes that the prosecution is not in the national interest; President Gerald Ford pardoned Nixon in part for this reason.

(Ashleigh Joplin/The Washington Post)

Or a president may conclude that even if a person may have committed a crime, he was acting in good faith to protect the national interest; President George H.W. Bush pardoned former defense secretary Caspar Weinberger in the Iran-contra affair in part for this reason.

In all such instances, however, the president is acting as a kind of super-judge and making a decision about someone else’s conduct, the justice of someone else’s sentence or whether it is in the national interest to prosecute someone else. He is not making a decision about himself.

Self-pardon under this rubric is impossible. The foundational case in the Anglo-American legal tradition is Thomas Bonham v. College of Physicians, commonly known as Dr. Bonham’s Case. In 1610, the Court of Common Pleas determined that the College of Physicians could not act as a court and a litigant in the same case. The college’s royal charter had given it the authority to punish individuals who practiced without a license. However, the court held that it was impermissible for the college to receive a fine that it had the power to inflict: “One cannot be Judge and attorney for any of the parties.”

The Constitution embodies this broad precept against self-dealing in its rule that congressional pay increases cannot take effect during the Congress that enacted them, in its prohibition against using official power to gain favors from foreign states and even in its provision that the chief justice, not the vice president, is to preside when the Senate conducts an impeachment trial of the president.

The Constitution’s pardon clause has its origins in the royal pardon granted by a sovereign to one of his or her subjects. We are aware of no precedent for a sovereign pardoning himself, then abdicating or being deposed but being immune from criminal process. If that were the rule, many a deposed king would have been spared instead of going to the chopping block.

We know of not a single instance of a self-pardon having been recognized as legitimate. Even the pope does not pardon himself. On March 28, 2014, in St. Peter’s Basilica, Pope Francis publicly kneeled before a priest and confessed his sins for about three minutes.

President Trump thinks he can do a lot of things just because he is president. He says that the president can act as if he has no conflicts of interest. He says that he can fire the FBI director for any reason he wants (and he admitted to the most outrageous of reasons in interviews and in discussion with the Russian ambassador). In one sense, Trump is right — he can do all of these things, although there will be legal repercussions if he does. Using official powers for corrupt purposes — such as impeding or obstructing an investigation — can constitute a crime.

But there is one thing we know that Trump cannot do — without being a first in all of human history. He cannot pardon himself.