Adam Liptak for the NYT:
The court rejected arguments from state lawmakers that their purpose in drawing the maps was not racial discrimination but partisan advantage.
The decision was the court’s latest attempt to solve a constitutional puzzle: how to disentangle the roles of race and partisanship when black voters overwhelmingly favor Democrats. The difference matters because the Supreme Court has said that only racial gerrymandering is constitutionally suspect.
Election law experts said the ruling would make it easier to challenge voting districts based partly on partisan affiliations and partly on race.