Chief Justice John Roberts appears to hold the key vote over whether the Supreme Court will allow the nation's first publicly funded religious charter school in Oklahoma.

Roberts was the only justice whose vote seemed in doubt after the court heard more than two hours of arguments Wednesday in a major culture-war clash involving the separation of church and state.

Four other conservative justices seemed firmly on the side of the St. Isidore of Seville Catholic Virtual School and the state charter school board that approved it.

The three liberal justices seemed just as likely to vote to affirm an Oklahoma Supreme Court ruling that held that the taxpayer-funded school would entangle church and state in violation of the First Amendment.

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Justice Amy Coney Barrett recused herself without explanation. Barrett previously taught law at Notre Dame and is close friends with Notre Dame law professor Nicole Garnett, a leading proponent of publicly funded religious charter schools.

If Roberts sides with the liberals, the court would be tied 4-4, an outcome that would leave the state court decision in place, but would leave the issue unresolved nationally.

If he joins his conservative colleagues, on the other hand, the court could find that the taxpayer-funded school is in line with a string of high court decisions that have allowed public funds to flow to religious entities. Those rulings were based on a different part of the First Amendment that protects religious freedom.

Liberal justices have complained that those decisions have eaten away at the separation of church and state.

The case comes to the court amid efforts, mainly in conservative-led states, to insert religion into public schools. Those include a challenged Louisiana requirement that the Ten Commandments be posted in classrooms and a mandate from Oklahoma’s state schools superintendent that the Bible be placed in public school classrooms.

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St. Isidore, a K-12 online school, had planned to start classes for its first 200 enrollees last fall, with part of its mission to evangelize its students in the Catholic faith.

Opponents warn a decision to allow the school to open would sap money from public schools and possibly upend the rules governing charter schools in almost every state.

The state board and the school are backed by an array of Republican-led states and religious and conservative groups, though the case has divided some of Oklahoma’s Republican leaders.

Gov. Kevin Stitt and Superintendent of Public Instruction Ryan Walters support using public funds for religious schools, while Attorney General Gentner Drummond has opposed the idea and sued to overturn the state board’s approval of St. Isidore.

A key issue in the case is whether the school is public or private. Charter schools are deemed public in Oklahoma and the other 45 states and the District of Columbia where they operate.

They are free and open to all, receive state funding, abide by antidiscrimination laws and submit to oversight of curriculum and testing. But they also are run by independent boards that are not part of local public school systems.

Just under 4 million American schoolchildren, about 8%, are enrolled in charter schools.