A little more than four years ago, the Supreme Court delivered a surprise victory to L.G.B.T.Q. communities. Rejecting the position of the Trump administration, the court ruled by a lopsided margin that a federal civil rights law protected transgender people from workplace discrimination.

In the intervening years, transgender rights have become a ferocious battleground in the culture wars, and controversies over health care, bathrooms, sports and pronouns played a prominent role in the presidential campaign. But the Supreme Court has had only glancing encounters with such issues since the employment discrimination case in 2020, which featured a majority opinion from Justice Neil M. Gorsuch, Mr. Trump’s first appointee to the court.

That will change on Wednesday, when the court hears its second major case on transgender rights, a challenge to a Tennessee law that prohibits some medical treatments for transgender youths.

It is the marquee case of the term. The court’s decision, expected by June, may determine not only the fate of the law and similar ones in more than 20 other states but also what role the Constitution’s equal protection clause has to play in cases claiming discrimination against transgender individuals.

The Tennessee law prohibits medical providers from prescribing puberty-delaying medication, offering hormone therapy or performing surgery to treat the psychological distress caused by incongruence between experienced gender and that assigned at birth. But the law allows those same treatments for other purposes.

The primary question for the justices is not whether Tennessee’s ban is wise or consistent with the views of medical experts. It is, instead, whether the law makes distinctions based on sex. If it does, a demanding form of judicial review — “heightened scrutiny” — kicks in. If it does not, the Tennessee law will almost certainly survive.

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