On Monday, the U.S. Supreme Court held oral arguments in an important religious freedom case. It involves a football coach at a public high school who says he was forced to leave his job after the school directed him to stop his practice of praying on the field after each game had ended.

The case is particularly important because it involves conflicting claims, each based on a different part of the First Amendment. The coach argues the school had interfered with his ability to act on his beliefs in violation of the Free Exercise Clause. The school says it cannot allow the prayer for fear it will be perceived as endorsing a religious practice in violation of the Establishment Clause.

That potential tension came up in the oral argument. An invaluable summary of the argument from SCOTUSblog suggests the majority of the justices seem sympathetic to the coach’s position. Important questions involved analogies to other actions such as kneeling during the national anthem, worries that students might feel pressure to participate in the post-game prayers, and the free speech implications of the school’s decision.

Among the important subjects discussed in the oral argument is the precise nature of the requirements of the Establishment Clause. At what point does an action in a school setting or by a school employee become an unconstitutional endorsement of religion?

This is particularly important since the lower courts found in favor of the school solely on the basis that it was constitutionally compelled to prevent the coach’s praying because it could be understood as the school endorsing religion. If the after-game prayer did not violate the Establishment Clause, then firing the coach over it would almost surely violate his rights to free speech and free exercise.

This explains a recurring theme (and source of puns) in the questioning: the “Lemon test.” This refers to a 1971 case, Lemon v. Kurtzman, in which the Supreme Court struck down laws in Pennsylvania and Rhode Island that gave direct public financial support to private religious schools. In doing so, the court created a three-part test for determining when a government action unconstitutionally establishes religion. According to the court, an action (1) must have a secular purpose, (2) must not have the effect of promoting or inhibiting religion, and (3) cannot create “excessive entanglement” between the state and religion. This last factor has proven hard to apply given its subjective nature.

As Justice Brett Kavanaugh said in the oral argument, it has not been applied in the past few decades. But it has reappeared in cases after seemingly being abandoned. In fact, Justice Antonin Scalia famously wrote about it:

Like some ghoul in a late-night horror movie that repeatedly sits up in its grave and shuffles abroad, after being repeatedly killed and buried, Lemon stalks our Establishment Clause jurisprudence once again, frightening the little children and school attorneys of Center Moriches Union Free School District. Its most recent burial, only last Term, was, to be sure, not fully six feet under: Our decision in Lee v. Weisman, 505 U. S. 577, 586-587 (1992), conspicuously avoided using the supposed “test” but also declined the invitation to repudiate it. Over the years, however, no fewer than five of the currently sitting Justices have, in their own opinions, personally driven pencils through the creature’s heart (the author of today’s opinion repeatedly), and a sixth has joined an opinion doing so.

Justices Kavanaugh and Neil Gorsuch both brought up the fact that Lemon has not been applied but also not overruled. This may be causing some of the problem in cases like this one. Paul Clement, the attorney for the coach, explained:

If it requires formally overruling Lemon and the endorsement tests that come from that, I think that would be very helpful. … [W]hat continues to happen is that there is overt discrimination on the basis of religion, as is evidenced in the record here, by school districts who aren’t evil. It’s just they’re doing it out of misguided endorsement concerns.

Kavanaugh suggested the test has already been abandoned, and Clement referenced the Scalia quote: “Sure, but … it’s a stubborn – it’s a stubborn fruit, and I don’t think just pushing a pencil through it has done the trick. I mean, you really have to slice it in half.”

Providing that kind of clarity may be one of the most important things the justices could do in this case.