The case concerned a constitutional puzzle: how to distinguish the roles of race and partisanship in drawing voting maps when Black voters overwhelmingly favor Democrats.
The Supreme Court cleared the way on Thursday for South Carolina to keep using a congressional map that a lower court had deemed an unconstitutional racial gerrymander that resulted in the "bleaching of African American voters" from a district.
The conservative majority, by a 6-to-3 vote, returned the case to the lower court, handing a victory to Republicans by allowing them to maintain boundaries that helped make the district in question a party stronghold.
The immediate effect of the ruling will be limited, as the court's delay in ruling had already ensured that this year's elections would take place under the contested map. But the majority opinion, written by Justice Samuel A. Alito Jr., will have an impact beyond South Carolina in the years to come, said Richard L. Hasen, a law professor at the University of California, Los Angeles.
"Justice Alito for a court majority has once again come up with a legal framework that makes it easier for Republican states to engage in redistricting to help white Republicans maximize their political power," Professor Hasen said.
The ruling was the latest in a series of closely divided decisions on elections that are a distinctive element of the work of the court led by Chief Justice John G. Roberts Jr., including ones that have amplified the role of money in politics, made it easier to restrict voting and exempted partisan gerrymandering from review in federal court.
The trend is not entirely uniform, as the court ruled last year that Alabama lawmakers had diluted the power of Black voters in drawing a congressional voting map. But the overall pattern has been to limit the oversight of elections by Congress and the federal courts, often in ways that have benefited Republicans.
In the case decided Thursday, Alexander v. South Carolina State Conference of the N.A.A.C.P., No. 22-807, the court's majority held that courts must generally credit lawmakers' assertions that their goal in redistricting was partisan, which is permissible, rather than based on race, which is not. "We start with a presumption that the legislature acted in good faith," Justice Alito wrote.