Unnoticed amid recent serial blockbuster oral arguments, the U.S. Supreme Court on March 20 issued a game-changer of a decision, portending large doctrinal and real-world reverberations.

On its face, Wos v. E.M.A. presented simply a brow-furrowing question about the federal Medicaid statute. But the court’s opinion reached out to resolve — or at least, to signal how a majority is prepared to resolve — an underlying issue at the heart of a contentious and highly consequential constitutional war.