Progressives have long looked to federal courts to guard the rights of racial minorities and dissenters. But that protection is weakening. Faced with the enormous injustice of partisan gerrymandering, the Supreme Court last month permitted politicians drawing election district maps to discriminate by party and even potentially mask their racial “packing” and “cracking” as mere partisanship. To fill this growing gap, reformers should take an unexpected route: states’ rights.

Chief Justice John Roberts wrote an opinion that allowed two gerrymanders, one committed by Republicans in North Carolina and one by Democrats in Maryland, to stand. His reason? He could not find a standard to judge when an offense had occurred. He rejected a considerable body of empirical research, including suggestions by my colleagues and me in an amicus brief.

Federalism, in which regional governments retain considerable power, has been invoked in the past to take away representational rights. But a local approach, properly applied, can also restore them. In a stinging dissent, Justice Elena Kagan pointed out that where the Supreme Court had failed to define and regulate partisan gerrymandering, four lower federal courts had succeeded.

State courts can do so, too — without federal approval. The elections clause of the Constitution gives states broad authority over redistricting as long as the actions do not run afoul of federal law. Chief Justice Roberts conceded that states can act on their own by “actively addressing the issue through state constitutional amendments and legislation.” Now that Republicans and their designates control the Supreme Court, the Senate and the presidency, reformers should embrace what Heather K. Gerken, the dean of Yale Law School, calls “progressive federalism.”