Drawing the boundary lines of legislative or congressional districts to provide an unfair advantage to one party is a practice with a long if not distinguished pedigree in American politics. The name for this process — gerrymandering — derives from Elbridge Gerry, a Massachusetts governor who in 1812 approved a redistricting plan that included a misshaped district resembling a salamander.

But sophisticated computer software has turned Gerry’s salamander into a true monster. It allows a party that controls the state legislature to perfect the art of map manipulation, ensuring that its candidates are elected in numbers obscenely out of proportion to its support statewide.

Fortunately, there are welcome signs that the tide is turning.

On Monday the Pennsylvania Supreme Court, which last month ruled that a congressional map drawn by the Republican Legislature violated the state constitution’s guarantee of “free and equal” elections, promulgated a new map that relies on advice from a Stanford University professor. Under the previous map, voters in 2016 cast ballots for Democratic and Republican House candidates in roughly equal numbers, yet 13 of the state’s 18 House seats went to Republicans. Under the new map, the delegation is expected to be more evenly divided. The new map also satisfies the court’s requirements for districts that are more compact and break apart fewer counties.

Meanwhile, in neighboring Ohio the Legislature has proposed a constitutional amendment that would establish a complicated new arrangement designed to involve both parties in the congressional redistricting process.

The U.S. Supreme Court aided the cause of reform with a 2015 ruling upholding the right of states to entrust the drawing of congressional district lines to independent commissions, as California does. Now, two new cases before the court provide an opportunity for the justices to go dramatically further and rule that some gerrymanders are so extreme that they violate the U.S. Constitution.

The first case, which was argued last October, involves a Republican-friendly map for the Wisconsin Assembly. The second, which will be argued March 28, focuses on a map fashioned by Democrats that allowed their party to capture a historically Republican seat in Maryland’s House delegation.

Looming over both cases is a 1986 Supreme Court decision holding that partisan gerrymandering could violate the 14th Amendment’s Equal Protection Clause if it intentionally and effectively discriminated against an identifiable political group. But the court has never agreed on a clear standard for deciding whether partisan gerrymanders cross that line.

The lack of guidance from the Supreme Court hasn’t stopped plaintiffs and lower-court judges from coming up with workable legal standards. In striking down the Wisconsin map, a three-judge federal court said that the U.S. Constitution was violated if a redistricting plan is “intended to place a severe impediment on the effectiveness of the votes of individual citizens on the basis of their political affiliation,” has that effect, and can’t be justified on other, legitimate grounds. The judges relied on both the Equal Protection Clause and the free-speech protections of the 1st Amendment.

Lawyers can argue about whether the justices should rely on the 14th Amendment or the 1st Amendment in striking down partisan gerrymanders. In fact, maps that disproportionately favor one party violate both political equality and free speech. What matters is that the court use its authority to end redistricting abuse by state lawmakers, because you can’t always count on state supreme courts to stop them. More than two centuries after Elbridge Gerry signed off on his “salamander” map, the day of reckoning for gerrymandering has arrived.