On March 28, the U.S. Supreme Court hears arguments in the Gloucester County School Board case, its first encounter with the growing transgender rights movement.

Journalists, it's time to work up those walkups.

The basics: The Obama administration’s Departments of Education and Justice notified all U.S. public schools last May that to qualify for continued federal funding they need to follow each student’s sense of personal “gender identity,” as opposed to birth biology, regarding access to “sex-segregated restrooms, locker rooms, shower facilities, housing and athletic teams (.pdf document here)."

That change redefined “sex” under Title IX of the anti-discrimination law in question. For 44 years before that, the government thought “sex” meant biological gender, not an identity that may conflict with it. In the current case, an anatomically female Virginia high schooler who is transitioning wants to use boys’ toilets instead of unisex facilities the school provides. Local school districts are caught between transgender rights appeals and community concerns about privacy and security.

The case’s significance is not ended by the February 22 decision of the incoming Donald Trump administration to rescind the Barack Obama directive for now. Access to locker rooms and showers are also part of this hot-button debate.

With gay marriage legalized throughout the United States by the Supreme Court, the LGBTQ movement is focusing all its moxie on transgender rights. The belief that gender is “assigned” at birth but flexible, rather than fixed by biology, gains cultural clout from important segments of the Democratic Party, big business, the academic world, the entertainment industry, professional and college athletics, and the like.

That poses a major challenge for advocates of religious liberty, already on the defensive with other issues.