A genuinely historic event takes place at the Supreme Court on Thursday. The justices hear arguments on Donald Trump’s claim that he is immune from prosecution after leaving office for any of his official acts while he was president. Specifically, Trump claims that the steps he took to block the certification of Joe Biden’s election were part of his official duties and that he thus cannot be criminally prosecuted.

The question of presidential immunity from criminal prosecution after leaving office has never been decided by the Supreme Court.

NPR special live coverage begins just ahead of the 10 a.m. Supreme Court hearing. Click on the player below to listen or tune in on the NPR app.

President Richard Nixon, while in office, was named an unindicted co-conspirator in the Watergate scandal, but he was not prosecuted then because the Justice Department concluded that under the Constitution, a sitting president could not be criminally prosecuted. Once Nixon resigned in 1974, however, and was no longer protected as a sitting president, he accepted a pardon from President Gerald Ford rather than face criminal charges.

Trump is making a far broader argument for immunity. He contends that he cannot be prosecuted — ever — for his “official acts” as president unless he is first impeached, convicted by the Senate and removed from office. He was impeached twice, but the Senate failed to muster the two-thirds vote needed to convict. So, were the Supreme Court to embrace Trump’s argument, it would mean, given modern political realities, that he and future presidents would likely be immune from prosecution after leaving office.

Trump’s definition of a protected official act is a broad one, as illustrated by an exchange between his lawyer, D. John Sauer, and Judge Florence Pan during arguments at the federal appeals court in Washington, D.C., earlier this year.

“Could a president order SEAL Team Six to assassinate a political rival?” Judge Pan asked, noting that an order given by the commander in chief to the military would be an official act.

Sauer replied that a former president could not be charged for giving such an order unless he had been “impeached and convicted first.”

The three-judge appeals court panel, including two Democratic and one Republican appointee, ruled unanimously against Trump on the immunity question in February. Trump then appealed to the Supreme Court, though the former president will not be there today because he is required to be at his New York trial on charges that allege he falsified New York business records in order to conceal damaging information to influence the 2016 presidential election.

A test for the high court

Although there are four pending criminal indictments against Trump, only one is before the Supreme Court on Thursday: special counsel Jack Smith’s case alleging that Trump knowingly and falsely sought to prevent Biden, the duly elected president, from taking office.

The high court case is more than a test for presidential immunity. It is also something of a test for the Supreme Court itself, on both substance and timing. After all, even if the court were to rule against Trump, if the justices drag their feet or send the case back to the trial court for significant further findings a Trump trial would be almost certainly impossible before the November election. And if he is elected for a second time, Trump could try to dismiss the case against him — or even pardon himself if he’s convicted.

Trump lawyer William Scharf maintains that everything the former president is accused of doing was an official act, and that after leaving office, Trump cannot be prosecuted for those acts. “What President Trump was trying to do was investigate election fraud in the aftermath of the 2020 election,” Scharf says.

Without presidential immunity, Scharf contends, “You end up in a scenario where presidents will be paralyzed by the fear of post-election criminal prosecutions, and the ability of the President to discharge his duties in a vigorous and effective way will be forever crippled.”

Not so, counters Peter Keisler, a who served as a top Justice Department official in the George W. Bush Administration: “You don’t protect the presidency by immunizing somebody who tries to steal it.”

Keisler has joined with several dozen high-ranking former GOP officeholders in filing a Supreme Court brief opposed to Trump’s position.

“The text of the Constitution has no provision granting this immunity. No court decision has ever recognized this immunity. The historical understanding in our country has always been exactly the opposite,” Keisler says. “Fundamentally, Trump’s argument’s just at war with the basic precept of our system that says that no one’s above the law.”

NYU law professor Trevor Morrison also pushes back at Trump’s claim that his actions surrounding the 2020 election were part of a president’s official duties. “The Constitution gives the President no role whatsoever in the administration of federal elections,” says Morrison, adding that the states, Congress, even the Vice President plays a role. But there is no mention in the Constitution of the President playing a role.

As for Trump’s claim that no president can be prosecuted unless he has been first been impeached, convicted and removed from office, Morrison calls that argument “preposterous.” Senate Republican Leader Mitch McConnell clearly rejected that idea when he voted against conviction in the second Trump impeachment.

“President Trump is still liable for everything he did while he was in office,” McConnell said in a speech on the Senate floor. “We have a criminal justice system in this country … and former presidents are not immune.”

But Trump lawyer Scharf contends that if the Supreme Court doesn’t put a stop to presidential liability now, “You’ll have an endless cycle of recriminations and prosecutions at the end of every presidency.” If Trump can be prosecuted after leaving office for what he did in seeking to void the election results, he says, then why not Biden for his handling of the border, Barack Obama for ordering drone strikes that resulted in American casualties, and George W. Bush for starting the Iraq War?

Trump rests much of his argument on a 1982 Supreme Court decision holding that presidents have absolute immunity from civil lawsuits for their official acts. But the court majority in that case emphasized that it was not deciding whether a similar immunity exists when it comes to criminal prosecutions.

The Trump briefs don’t include any significant discussion of the Nixon tapes case

In that landmark decision, the court ordered Nixon to turn over to prosecutors specific White House tape recordings in which Nixon, then still president, plotted to cover up various campaign crimes, including the attempted bugging of the Democratic National Committee offices. When the White House tapes eventually became public, they led inexorably to a House committee vote to approve articles of impeachment and Nixon’s ultimate resignation.

Still, Thursday’s case is not a slam dunk for the prosecutors. NYU’s professor Morrison says it’s “significant” that three members of the court — Chief Justice John Roberts and Justices Elena Kagan and Brett Kavanaugh — previously served in the White House and were “responsible for attending to questions of presidential prerogatives and presidential power.”

Kavanaugh has actually been on both sides of these issues. He played an important role in the special counsel’s investigation of the sex scandal involving President Bill Clinton, but more importantly, he served first as as associate counsel and then for three years as staff secretary for President George W. Bush.

With that in mind, the brief filed by the group of former GOP officeholders has advanced something of a middle ground. It rejects presidential immunity for federal crimes undertaken by a president on or after Election Day in order to usurp the legitimate results of a democratic election.

On “the particular facts of the case, where the charge is that he unlawfully tried to seize the presidency after losing the election, it’s sufficient to say there’s certainly no presidential immunity … for crimes like that,” says Peter Keisler.

That would leave undecided tricky immunity questions involving presidential decisions centered on foreign relations or use of the military abroad.