GOP leaders are calling for religion in public schools. It's not the first time.

Oklahoma's top education official ordered public schools to teach the Bible and wants state funding for a controversial religious charter school. Louisiana leaders directed schools to display the Ten Commandments. Texas leaders proposed a curriculum that incorporates biblical lessons.

Authorities in these Republican-led states are confidently taking on constitutional protections that bar religious instruction from public education. School administrators and civil rights advocates are pushing back, saying these mandates violate students' rights.

In states where evangelical Christians make up a sizeable portion of constituents, incorporating Bible teachings into the curriculum has gained traction, said Ira C. Lupu, a professor at George Washington University School of Law who has written on religion in the First Amendment.

During this moment in American history, a legal challenge to one of these measures in the U.S. Supreme Court could land differently than in other eras., Lupu said. The new policies, he said, have a better shot at prevailing before the court's conservative majority.

None of these mandates have advanced to that stage yet. Parents in Louisiana sued in June, challenging the policy requiring schools to display the Ten Commandments. But the case remains at the trial court level.

Louisiana Gov. Jeff Landry and Ryan Walters, the superintendent of education in Oklahoma, say they are prepared to take on legal challenges from people who disagree with them. Walters told USA TODAY he believes the Supreme Court will uphold the mandate requiring religious education if someone sues and a case makes it there. He credits President Donald Trump with being outspoken and building support for the movement during his 2024 presidential campaign.

"The support from Trump has given us this opportunity," Walters said in an interview with USA TODAY.

Leaders in other Republican-run states have contacted Walters about Oklahoma's plan, he said, which he considers a modern-day "blueprint" for codifying the teaching of the Bible in public schools.

What began campaign to bring religion into schools?

The Supreme Court ruled in two separate cases in the 1960s that school-sponsored prayer and religious teaching in school violated the Establishment Clause of the First Amendment, which says the federal government cannot make laws governing the "establishment of religion" or prohibiting "the free exercise thereof."

The U.S. Department of Education has interpreted that to mean that public schools "may not provide religious instruction" in a devotional manner or "prescribe prayers to be recited by students or by school authorities."

If educators teach about religion as an academic subject, they must promote religious liberty and respect all religious views, including the views of those who don't believe, the federal agency says.

Court cases challenging the use of the Bible, Ten Commandments and religious materials in classrooms have continued to crop up in the years since.

One of the most influential rulings came in 1971 when the Supreme Court ruled in Lemon v. Kurtzman that constitutional protections requiring the separation of church and state apply to public schools.

In his majority opinion, Chief Justice Warren Burger said laws about bringing religion into schools needed to pass a three-part test:

• They must "have a secular legislative purpose"
• Their "principal or primary effect must be one that neither promotes nor inhibits religion"
• And, they must not foster “excessive government entanglement with religion.” 

"Schools have repeatedly violated these criteria, resulting in a steady stream of litigation," wrote Jill Heinrich, a professor of education at Cornell College, in an article for the school.

Over the last several decades, more than a dozen states tried to implement laws requiring the Ten Commandments in schools.

The Supreme Court ruled in 1980 in Stone v. Graham that a Kentucky law requiring schools to display the Ten Commandments was unconstitutional because it violated the Lemon v. Kurtzman test.

Since then, Arizona, Mississippi, Oklahoma, South Carolina, Texas and Utah have proposed measures requiring the Ten Commandments to be displayed in classrooms at schools.

Gov. Katie Hobbs vetoed the Arizona bill mandating displays of the Ten Commandments. Utah made it optional for schools to post them. A proposal in Oklahoma to make the displays optional died earlier this year when it wasn’t heard by a state House subcommittee.

The current groundswell to make the Bible and the Ten Commandments a mainstay at public schools represents a shift, said Lupu, the George Washington University constitutional scholar. He views it as evangelical Christians taking advantage of an opening before a conservative majority on the high court.

What's happening in Oklahoma schools?

At a state board of education meeting on June 27, Walters gave a directive to school leaders in Oklahoma: "Every teacher and every classroom in the state will have a Bible in the classroom and will be teaching from the Bible in the classroom."

At least 14 Oklahoma districts and the state teachers union rebuked Walters' directive to incorporate the Bible and the Ten Commandments into classes. They sent letters to parents saying they didn't plan to change the curriculum or teach the Bible despite the new requirements.

The Oklahoma Attorney General’s Office said state law already allows the Bible to be taught in classrooms, and districts have the right to choose whether they'll teach it this fall.

The Center for Education Law issued a memorandum to Oklahoma school districts calling Walters’ mandate invalid under state law, citing it as a local control issue.

But Walters says opting out is not an option.

"They will teach it because they don’t get to choose what they teach," he told USA Today. Walters said at a recent school board meeting he would hold accountable any districts that refused to comply.

People suing the state over Walters' directive could hit roadblocks because the mandate's instructions on how the Bible should be taught are not uniform, Lupu said. This means educators have lots of latitude to interpret what it means to "teach about the Bible."

The American Civil Liberties Union contends the government shouldn't be investing in Bibles. The organization said it was joining other civil rights groups in calling for Oklahoma officials to hand over records related to the mandate, including documentation showing how the state plans to pay for copies of the Bible.

“Courts have repeatedly ruled that it is unconstitutional for public schools to coerce anyone to support or participate in religion or its exercise,'" Megan Lambert, ACLU of Oklahoma Legal Director, said in the news release. "Oklahoma children have the right to attend public school and to access the full range of school services without having government-sponsored religion imposed on them."

The Freedom From Religion Foundation, among the groups requesting the records, has been working to keep public institutions, including schools, secular for decades.

Patrick Elliott, the nonprofit's legal director, believes a "significant effort to push religion on other people's children in schools" stems from a wave of "Christian nationalism."

"All students are welcome at schools and when there are state efforts to really get them to believe in a certain brand of Christianity, that coerces students into religious practices and inhibits their religious liberties," he said.

At least 8 large Oklahoma districts:Rebuke superintendent's order to teach Bible

Ten Commandments in Louisiana schools

The dispute is different in Louisiana because the order issued to schools was specific and uniform: Every classroom must display the Ten Commandments.

When Landry, the governor, signed the Louisiana bill in June he quipped that he was prepared to respond if anyone had any concerns.

“I’m going home to sign a bill that places the Ten Commandments in public classrooms,” Landry said in June. “And I can’t wait to be sued.”

Louisiana parents and civil liberties groups went on to sue the state, saying that requiring the Ten Commandments violates the First Amendment.

"Permanently posting the Ten Commandments in every Louisiana public-school classroom – rendering them unavoidable – unconstitutionally pressures students into religious observance, veneration, and adoption of the state’s favored religious scripture," the complaint says.

In response, Louisiana has agreed to delay posting the Ten Commandments in public schools until at least November. The litigation is ongoing.

Ten Commandments posters won't go:In Louisiana classrooms until November

Contributing: Minnah Arshad, Greg Hilburn, Vivian Jones, George Petras; The USA Today Network

Contact Kayla Jimenez at kjimenez@usatoday.com. Follow her on X at @kaylajjimenez.