The original “gerrymander” in early 19th-century Massachusetts has now given way to more sophisticated efforts to skew legislative maps, which are under judicial scrutiny. Photo: Bettmann Archive/Getty Images

The recent decision of the Pennsylvania Supreme Court to overturn and redraw a congressional map it deemed an unconstitutional partisan gerrymander by the GOP-controlled legislature illustrates a big and important trend in efforts to provide fair redistricting, just before a new decennial cycle begins.

Public (and sometimes judicial) opinion has long been scandalized by the common practice of partisan gerrymandering (particularly when it comes to state legislators drawing their own districts). But until quite recently, the focus of redistricting reform was on who drew the maps and what they looked like to the untrained eye. It’s not surprising that the most prominent national redistricting reform initiative has long been legislation developed by former Tennessee congressman John Tanner (reintroduced regularly after his 2010 retirement by Tennessee colleagues).

The Tanner bill would require that redistricting decisions be made by independent commissions whose members are appointed by the legislatures with formal responsibility for drawing maps. It also requires that the commissions to respect wherever possible what are generally called “traditional redistricting principles” such as compact and contiguous districts. This latter guideline was meant to avoid the unsightly lashed-together districts that gave “gerrymandering” (identified with early 19th-century Massachusetts pol Elbridge Gerry, who was complicit in drawing a district that looked like a salamander) its very name.

Despite the perennial popularity in good government circles of Tanner-style redistricting reform, its limitations have also become obvious. Thirteen states currently deploy some kind of independent redistricting body with responsibility for redistricting (though six of them do not handle congressional maps). But to the extent that members are appointed by partisan pols, their “independence” is perpetually suspect.

It’s also increasingly clear that the finely grained data available to map-drawers, which they can manipulate via sophisticated software, has made “traditional redistricting principles” less effective in combating gerrymanders. The Pennsylvania case in the news right now provides a great illustration: After the state Supreme Court told the legislature to come up with a new congressional map that was less partisan and also less disruptive of traditional redistricting principles, the solons promptly came up with a map that looked a lot neater and nicer but was just as partisan as the original.

So the Pennsylvania court emulated a federal district court in Wisconsin in looking beyond the usual considerations and challenging partisan gerrymanders not for how they were devised but for their partisan impact. And like that Wisconsin federal court, the Pennsylvania state court relied on new measurements of partisanship — notably a social science tool called “efficiency gap” — to measure the effect of partisan gerrymandering and determine an appropriate standard.

That’s why the timing of the Pennsylvania court intervention is so interesting. The U.S. Supreme Court is expected to rule on the Wisconsin case — and on an alleged Democratic partisan gerrymander in Maryland, which a district court in that state refused to overturn — before the current term’s end in June. And the decision is expected to turn, as is so often the case, on the views of Justice Anthony Kennedy, who in the last big gerrymandering case (Vieth v. Jubelirer) back in 2004, fretted over the lack of a workable standard for partisan bias.

Kennedy was also looking for a “limited and precise rationale … to correct an established violation of the Constitution in some redistricting cases.” He didn’t find one in that case, ruling against Democrats challenging a Republican gerrymander in the state. But he signaled he would be open to striking down extreme partisan gerrymanders if the court could agree on a standard to do so, like in racial gerrymandering cases where it’s possible to prove a clear violation of the Voting Rights Act.

Voting rights advocates are hoping that time has come.

Whatever SCOTUS is or is not planning, the Pennsylvania decision is probably a done deal, and could serve as an inspiration to state courts elsewhere with similar state constitutional provisions guaranteeing equal protection of the laws and equal voting rights. Yes, Republicans are trying to get the decision thrown out on grounds that the Pennsylvania judges are usurping the legislature’s U.S. Constitutionally established power over redistricting. But SCOTUS has already rejected an emergency appeal on that basis, and one voting rights expert called the GOP legal effort “the mother of all Hail Marys in terms of its likelihood to succeed.”

And if SCOTUS does rule in favor of the gerrymandering challengers, it could have a large impact on the next round of redistricting due to begin in 2021, whether or not it has the kind of effect on 2018 House races that Democrats hailing the Pennsylvania decision hope for. We don’t know yet which party will control the legislatures and governorships in states like Wisconsin, Florida, North Carolina, and Ohio (among the most egregious gerrymanderers last time around) after 2020. But it’s possible there will be more stability in congressional maps than we’ve seen in recent years, whether or not they are neat and nice or were drawn up by commissions alleged to be non-partisan.