The beginning of the end of the separation of church and state started with recycled tires—specifically, recycled tires used for playground padding at a Missouri church’s preschool. The end could arrive this summer, in the form of a Supreme Court ruling requiring Oklahoma to fund the nation’s first religious charter school, a Catholic institution that is “faithful to the teachings of Jesus Christ.”

The Constitution provides that the government “shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.” The Court has said the two religion clauses are intended to facilitate religious practice “without sponsorship” (the establishment clause) and “without interference” (the free-exercise component). But there are occasions, particularly when it comes to matters of government funding, when those clauses are in tension with each other. As the court has grown increasingly conservative in recent years, it has consistently resolved this conflict in favor of free exercise, expanding the sphere of what protecting religious liberty requires and constricting, to the point of near-invisibility, the scope of what the establishment clause forbids.

Which brings us back to tires. In 2017, the Justices considered a claim by Trinity Lutheran Church of Columbia. Its preschool and daycare center had been excluded from a Missouri playground resurfacing program; the church claimed that this infringed on its religious freedom. The Court ruled 7–2 for the church. “The exclusion of Trinity Lutheran from a public benefit for which it is otherwise qualified, solely because it is a church, is odious to our Constitution,” the Court said in a decision by Chief Justice John Roberts. Justice Elena Kagan joined the majority, and Justice Stephen Breyer concurred separately, emphasizing that the program was akin to providing churches with police and fire protection.

Justices Sonia Sotomayor and Ruth Bader Ginsburg dissented, and in hindsight their warning looks prescient—it’s not only playground surfaces that can be slippery. “To hear the Court tell it, this is a simple case about recycling tires to resurface a playground. The stakes are higher,” Sotomayor wrote. “This case is about nothing less than the relationship between religious institutions and the civil government—that is, between church and state. The Court today profoundly changes that relationship by holding, for the first time, that the Constitution requires the government to provide public funds directly to a church. Its decision slights both our precedents and our history, and its reasoning weakens this country’s longstanding commitment to a separation of church and state beneficial to both.”

A footnote in the Missouri ruling noted that it did not “address religious uses of funding.” That distinction didn’t last long. As Sotomayor predicted, playground padding was just the start. Three years later, in 2020, the Court ruled that a Montana tax-credit program for private-school tuition had to include religious schools. This time, all four liberal Justices dissented. In a 2022 case from Maine, the conservative majority, bolstered to six with the arrival of Justice Amy Coney Barrett, went even further. In parts of the state so rural that there are no public high schools, Maine pays for students to attend other public or private schools, but not sectarian ones. The Court said that limitation violated the rights of parents who wanted their children to receive a religious education. “What a difference five years makes,” Sotomayor lamented in a dissent. “Today, the Court leads us to a place where separation of church and state becomes a constitutional violation.”

Now comes Oklahoma, where the Catholic Church created St. Isidore of Seville Catholic Virtual School is seeking state recognition to become an explicitly religious charter school. The state’s current charter schools include a science-and-technology-focussed school, a Cherokee-language immersion program run by the tribe, and a “classical academy” sponsored by conservative Hillsdale College. St. Isidore, named for a sixth-century Spanish theologian, would be something entirely different from any publicly chartered, publicly funded school that has come before. According to a proposed curriculum guide, kindergartners would be taught that “they can communicate with God through prayer,” and first graders instructed on the Mass and “the reality of sin.” The “teachings of Jesus Christ as set by the Catechism of the Catholic Church” would “permeate the School day,” braided through the secular curriculum. Introductory high-school science would “reveal God’s orderly creation of the universe,” while physiology would adopt “a faith-based approach to the value of human life from the beginnings of a cell.” The school would be open to all applicants, whether Catholic or not, but students would be required to attend Mass.

Oklahoma’s Statewide Charter School Board granted approval to St. Isidore, but the state’s Republican attorney general—Gentner Drummond, who is now running for governor—sued to block that action. The Oklahoma Supreme Court agreed that allowing St. Isidore to operate as a public Catholic charter school would violate both the establishment clause and the state constitution’s ban on spending government funds to support religious institutions. Notably, the court, which has five justices named by Republican governors and three named by a Democrat, divided 6–2 on the issue.

Things may be trending in a different direction at the U.S. Supreme Court, judging by the oral arguments held before the Justices on Wednesday. Lawyers for St. Isidore and the Charter School Board argued that refusing to open the charter-school program to religious schools violates the free-exercise clause. They described St. Isidore as a private institution simply seeking access to a program available to all but those with religious affiliations—much like the Missouri preschool in the playground case. No families are forced to subject themselves to its curriculum; they are given a choice among various schools. On the other side, Gregory Garre, who served as George W. Bush’s Solicitor General and is representing Drummond, contended that charter schools are public schools, and that teaching religion as truth in public schools has long been impermissible under the establishment clause. Even as St. Isidore complained of being singled out for unfavorable treatment because of its religious status, Garre noted, the school was asserting that it deserved an exemption from ordinary rules that require charter schools to agree not to discriminate in hiring. The school said, instead, that it “complies with all applicable state and federal laws and statutes to the extent the teachings of the Catholic Church allow.”

Significantly, St. Isidore is down a Justice who would likely be inclined in its direction. Barrett recused herself from the case without explanation; it was presumably because of her connection to Nicole Stelle Garnett, a former Notre Dame colleague and close friend of hers who has been a leading proponent of religious charter schools and who advised St. Isidore. Barrett’s absence means the three liberal Justices, who would likely vote against the school, could prevail in an alliance with just one of the conservatives, because a 4–4 tie would leave the Oklahoma Supreme Court ruling in effect. Even so, Wednesday’s session was not encouraging for those who had hoped an expressly religious charter school would be a step too far, even for this conservative Court.