On October 4, Judge Susan Bolton will hold a hearing to consider former Sheriff Joe Arpaio’s request that she vacate his conviction for criminal contempt now that President Trump has issued what many have described as a regrettable but valid pardon. This choice is to Judge Bolton’s credit: Instead of simply vacating his conviction, she’s wise to grapple with this unusual and perhaps unprecedented pardon. And, to help her do so, she should appoint an amicus curiae, a “friend of the court.” Without one, Judge Bolton will hear only one perspective: Arpaio, of course, wants to see his conviction wiped away; and his former prosecutors at the Justice Department – the same Justice Department whose Office of the Pardon Attorney formally issued Arpaio’s pardon – surely will no longer take a contrary view, despite at least one valiant plea to do otherwise. Our legal system thrives on adversarial argumentation, and Judge Bolton deserves to hear two sides of the argument, not just one, as she thinks through how to handle Arpaio’s circumstances.

Why hold a hearing in the first place? Even though the President has issued a putative pardon, that pardon is generally viewed as not “self-executing.” That is, the action taken by the executive branch still needs to be “executed,” here by the judicial branch. It’s almost a translation function, and one that involves turning the piece of paper issued by the President into something meaningful within the context of the courts and the broader criminal justice system: turning a pardon into an actual wiping away of Arpaio’s existing conviction. Here’s the explanation provided by the Justice Department’s Office of the Pardon Attorney:

Does a presidential pardon expunge or erase the conviction for which the pardon was granted? No. Expungement is a judicial remedy that is rarely granted by the court and cannot be granted within the Department of Justice or by the President. Please also be aware that if you were to be granted a presidential pardon, the pardoned offense would not be removed from your criminal record. Instead, both the federal conviction as well as the pardon would both appear on your record. . . . If you are seeking expungement of a federal offense, please contact the court of conviction.

Few, I suspect, would have been surprised had Judge Bolton simply granted Arpaio’s motion to vacate his conviction without entertaining further discussion of it. Indeed, doing so would have been viewed by many as entirely consistent with a long tradition of viewing a president’s pardon authority as “plenary,” even “absolute.” That view is, to be sure, the inherited wisdom. And, perhaps, it ultimately dictates the outcome in Arpaio’s case, leaving the only response to the pardon available to another branch of government to be, at least conceivably, impeachment.

But it’s always the hard cases that challenge the inherited wisdom, and Arpaio’s pardon presents, at a minimum, a hard case. Trump’s move has certainly proven controversial, but it’s also generated interesting arguments from legal experts about how it should be handled. Judge Bolton deserves to hear those arguments fully fleshed out, no matter what result she ultimately deems proper. In the end, if she simply vacates Arpaio’s conviction (as most anticipate she will), then her doing so will be on more solid ground in light of her having explored fully the alternatives.

And there are interesting questions to explore. For example, does Arpaio’s pardon leave the door open for his prosecution for lesser offenses, should the current Justice Department – or, much more likely, a future Justice Department – be inclined to pursue them? Does the pardon have any consequences on potential prosecutions under state law? Does Supreme Court precedent describing acceptance of a pardon as “confession” of guilt mean that Arpaio’s embrace of his pardon can be invoked in new civil suits against him for damages by those who suffered at his hands?

And there are intriguing questions facing Judge Bolton regarding the immediate question before her – whether to vacate Arpaio’s conviction based on Trump’s ostensible pardon. While many legal scholars, even liberal ones, have characterized Trump’s pardon as deeply regrettable but likely lawful, other commentators have alleged that Trump’s pardon was a due process violation, or an equal protection violation, or obstruction of justice – or some combination thereof. As it were, I think there’s another argument worth having an amicus explore: that Trump’s pardon was unconstitutional and invalid as an attempt to override a constitutional determination regarding Arpaio’s behavior already made by our federal judiciary.

Under this line of argument, as with Trump’s travel ban, the unconstitutional nature of Trump’s action would emerge from the combination of what he did and what he said about what he did. Just as judges across the country, backed by legal scholars, have looked to Trump’s public words to evaluate the lawfulness of the travel ban, Judge Bolton, aided by an amicus, could look to Trump’s statements about why he sought to pardon Arpaio to assess whether Trump did so consistent with the Constitution. (Utilizing an amicus would avoid the potential constitutional complications of the court appointing an independent special prosecutor, as has recently been suggested.)

An amicus could begin by laying out the basics. Many already agree that, however expansive a president’s pardon authority might be, it has at least some limits. If a president pardoned only white convicted criminals based on the color of their skin, that presumably would be a violation of the Constitution’s guarantee of “the equal protection of the laws,” potentially giving rise not only to impeachment but also conceivably calling into question the validity of the pardons granted. If a president pardoned someone in exchange for a bribe, that presumably would be a violation of the criminal law, which could also cast doubt on the pardon’s validity. All told, the pardon authority may be extensive, but it’s not necessarily unlimited.

So, what would an amicus argue that Trump did wrong here? He refused to accept the pronouncement of the federal judiciary – the branch of our Federal Government charged with ultimately saying what the Constitution means – when that branch of government had already spoken to the constitutional question at issue.

An amicus could help Judge Bolton place in constitutional context the sequence of key events. First, in 2011, Judge G. Murray Snow determined that Arpaio was violating the Constitution by systematically targeting for traffic stops those who looked Latino and detaining those who were deemed undocumented, and ordered Arpaio to stop. Second, Arpaio, rather than appeal the ruling to contest the judicial determination, by his own admission simply continued these “saturation patrols.” Third, Judge Bolton found Arpaio guilty of criminal contempt for violating Judge Snow’s order and thus continuing to violate the Constitution. Fourth, before Arpaio was even sentenced, President Trump pardoned Arpaio and – here’s the key – said, in the official White House statement announcing the pardon, that, “[t]hroughout his time as Sheriff, Arpaio continued his life’s work of protecting the public from the scourges of crime and illegal immigration.” And that was after Trump had previewed, just a few days before, his view of the matter at a rally in Arizona: “Was Sheriff Joe convicted for doing his job? I’ll make a prediction: I think he’s going to be just fine.”

The problem, the argument would go, arises when you view step four – Trump’s pardon of Arpaio for “doing his job” and acting responsibly “[t]hroughout his time as Sheriff” – in light of step one. At step one, a judge speaking on behalf of the judicial branch of our government held that Arpaio had violated the Constitution, not just once but repeatedly. At step four, Trump said Arpaio had been doing his job. That may be Trump’s view; but it’s not clear that he has the constitutional authority to act on it, even when invoking his formidable pardon power, once the judiciary has said precisely the opposite.

An amicus could also help Judge Bolton think through hypotheticals and counterfactuals, as any judge likes to do. For example, this all might be different if Trump had said he was pardoning Arpaio solely because Trump viewed him as factually innocent (that is, because Trump believed Arpaio did not systematically target Latinos for traffic stops), or as an old man now showing remorse, or even as a longtime public servant who’d redeemed himself in other ways. This might even be different if Trump simply said, echoing President Ford in pardoning former President Nixon, that Trump simply wanted to put this whole thing behind us. But that’s not what Trump said: Trump said Arpaio had been doing his job as sheriff all along. But the federal courts had said the opposite – because Arpaio had been violating the Constitution. Thus, an amicus could help frame what’s distinctive about Arpaio’s circumstances, and what tough issues that might arise in other circumstances Judge Bolton could leave for another day.

All in all, an amicus could argue that, when it comes to the showdown between the courts and the President crystallized by Trump’s pardon, the Supreme Court has said it’s the courts that prevail. Over the past half-century, the Court has increasingly described the federal judiciary as the ultimate interpreter of what the Constitution means. And it’s those pronouncements from our highest Court that, an amicus might argue, should tip the scales of justice toward Judge Snow and away from President Trump.

It would be important for the amicus to explain that this isn’t the only conceivable view of who gets the final word on the Constitution. Abraham Lincoln, perhaps our country’s finest constitutional scholar and teacher, at times adopted a “departmentalist” view of constitutional interpretation, in which no branch’s interpretation would necessarily override another’s. But even Lincoln accepted that the judiciary got the last word on the parties to a case before it; and, whatever the strengths or weaknesses of the departmentalist view, it’s the Supreme Court that’s told us with increasing clarity that the judiciary gets the last word on constitutional interpretation. In the famous words of Marbury v. Madison, “It’s emphatically the duty of the Judicial Department to say what the law is,” words that Chief Justice Warren later interpreted as establishing “the basic principle that the federal judiciary is supreme in the exposition of the law of the Constitution, and that principle has ever since been respected by this Court and the Country as a permanent and indispensable feature of our constitutional system” (emphasis added). That now-entrenched view of judicial supremacy could mean that Judge Snow, backed by Judge Bolton, simply can’t – constitutionally – be trumped by Trump.

Critical to the work of an amicus here would be exploring the Court’s precedent specifically on the pardon power. The leading case remains 1925’s Ex parte Grossman. That case established that a president can pardon a conviction for criminal contempt, just as Trump did for Arpaio. But it’s the underlying violation, not the contempt order sitting on top, that distinguishes Grossman from Trump’s putative pardon of Arpaio. A federal court had deemed Grossman to be running a speakeasy contrary to the law at the time and barred him from doing so. Another court found he’d continued to do so and therefore held him in contempt. President Coolidge pardoned Grossman to reduce his punishment to a fine because the President viewed imprisonment as too harsh a sentence for operating a speakeasy. That fits one traditional pardon paradigm: The President steps in to show leniency based on the particular facts of a case.

Trump’s pardon of Arpaio may be distinguishable from that. By his own account, Trump thinks Arpaio simply did nothing wrong. In this instance, the argument would go, that’s not Trump’s prerogative to determine, once the federal judiciary has found precisely the opposite by speaking to what the Constitution means in this context. Grossman itself explains that “[e]xecutive clemency exists to afford relief from undue harshness or evident mistake in the operation of enforcement of the criminal law” (emphasis added). And that’s just what Coolidge offered Grossman – some relief from enforcement of the criminal law. Trump, however, has attempted to overrule the federal judiciary’s very interpretation of the Constitution. And that, an amicus might argue, would run headlong into the separation of powers our country rightly holds so dear.

Judge Bolton deserves praise for taking her time to think through what to do with the unfortunate and perhaps unprecedented piece of paper issued by the President to Arpaio, as well as what others – such as federal prosecutors, state prosecutors, and civil litigants – might do with it in the future. She deserves help, and that’s why she should appoint an amicus to provide it.