In the next few months, the Supreme Court is expected to rule, at last, on one of the most corrosive practices in modern American democracy — the drawing of legislative district maps to entrench the party in power, no matter how many voters might want a different result. Even as this behavior, known as partisan gerrymandering, has gotten out of control in recent decades, the court has refused to rein it in because, the claim goes, any possible fix lies with the political branches and not the courts.

That’s bunk. The justices will see why if they look at what’s happening in several states where lawmakers have been holding clinics in self-interested mapmaking.

Both Democrats and Republicans draw biased maps, of course — the two cases before the Supreme Court this term make that clear — but modern partisan gerrymandering is mostly the work of Republicans, who control a majority of governorships, as well as the legislative chambers in 32 states. Their efforts to lock in this advantage by any means necessary — including by kneecapping any institutions, including the courts, that try to stop them — are the work of a party that has become, as the political scientists Norm Ornstein and Thomas Mann put it in 2012, “dismissive of the legitimacy of its political opposition.” At stake are not just hundreds of state legislative seats, but also control of the House of Representatives, which Republicans currently hold by a 45-seat margin.

The most shocking case is playing out right now in Pennsylvania, where Republican lawmakers in 2011 created maps so skewed that when Democrats won a majority of the popular vote the following year, it translated into only five of the state’s 18 congressional seats.