“The partisan gerrymanders here debased and dishonored our democracy, turning upside-down the core American idea that all governmental power derives from the people,” Kagan wrote. “These gerrymanders enabled politicians to entrench themselves in office as against voters’ preferences. They promoted partisanship above respect for the popular will. They encouraged a politics of polarization and dysfunction. If left unchecked, gerrymanders like the ones here may irreparably damage our system of government. And checking them is not beyond the courts.”