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The case is named for Kendra Espinoza, a single mother who lives near Kalispell, Montana, who took her two daughters out of public school after one struggled academically and the other faced repeated bullying. She enrolled her girls in a private school, Stillwater Christian, but, like the two other mothers named in the case, Espinoza struggled to pay tuition on her income as an office assistant and night janitor. In 2015, the Montana legislature created a scholarship incentive program to help families send their kids to private schools, religious or secular, which Espinoza says she looked forward to using. Before that could happen, however, the state department of revenue put a rule in place banning the program’s funds from being used at religious schools, saying that would violate Montana’s constitution.

The Supreme Court has to decide whether the kind of no-aid provision found in Montana’s state constitution runs afoul of the U.S. Constitution. For nearly two decades, the Court has held that state voucher programs can include religious schools if a particular state wants the inclusion. Should justices rule in favor of Espinoza and the other parents in this case, they would be taking that principle a step further: If states want to have a voucher program, they can’t exclude religious schools from participating.

It was inevitable that the Court would hear this kind of case eventually, Richard Garnett, a law professor at the University of Notre Dame, told me. Four or five decades ago, the Court was much more hostile toward voucher programs than it is today: The justices thought “aid to religious schools itself is suspect,” he said. Eventually, the Court softened this posture, in 2002 ruling in favor of an Ohio program that allowed state money to be used for tuition at private religious schools. Then, two years ago, the justices ruled in Trinity Lutheran Church v. Comer, deciding by a vote of 7 to 2 that states could not exclude religious organizations from participating in neutral state programs, such as a grant for resurfacing playgrounds. Although the justices bent over backwards to make the limits of their decision clear, “everybody who read that knew: Of course we’re talking about other forms of aid,” Garnett said. “Everybody knew the next case was going to be one involving school funding.”

The stakes of the Court’s decision in Espinoza could reach far beyond Montana. More than 30 states have similar provisions banning public aid to private religious schools, according to a brief filed by the Becket Fund for Religious Liberty. These measures have long been a target of ire for religious-freedom advocates: Many came about during a late-19th-century wave of anti-Catholic legislation, when politicians stoked fear about Catholics’ inability to place their duties as U.S. citizens over their allegiance to the pope. These provisions are generally referred to as Blaine amendments, after Representative James Blaine, who tried and failed to secure a federal constitutional amendment banning government aid to sectarian schools. The Supreme Court should find these measures unconstitutional, lawyers for Becket and other groups argue, so that states can craft “public programs without being weighed down by the bigotry of the past.”