On Thursday, Pennsylvania's state Supreme Court granted a petition to take jurisdiction over a lawsuit challenging its Republican-drawn congressional map as an illegal partisan gerrymander. A GOP-dominated lower court had previously stayed the lawsuit, but plaintiffs appealed to the high court, whose Democratic majority just expedited the proceedings and gave the lower court a deadline of Dec. 31. If the courts strikes down this map, Democratic Gov. Tom Wolf could veto any replacement GOP gerrymander, forcing the courts to draw nonpartisan districts in time for the 2018 midterms and presenting Democrats with opportunities for major gains.
As shown in the map at the top of this post, the GOP’s brazenly tortured lines have produced a stable 13-to-5 Republican congressional majority in what is otherwise an evenly divided swing state. That Republican advantage persisted even when Obama carried Pennsylvania by 5 points—and Democratic House candidates won more votes statewide than Republicans—in 2012, and it held fast in 2016 when Trump narrowly won the state. As we have demonstrated, this Republican gerrymander likely cost Democrats up to four seats in both 2016 and 2012, making it one of the most effective GOP gerrymanders nationally.
The plaintiffs in this suit pointed to several statistical tests to argue that Republicans could not have possibly passed the map that they did without intending to favor their own party. These tests include the “efficiency gap,” which is at the center of an upcoming U.S. Supreme Court case regarding Wisconsin, as well as one called the “mean-median district test,” both of which we have previously explained in detail. The plaintiffs have also put forth computer-simulated nonpartisan plans to buttress their claim that any efforts by mapmakers to adhere to traditional redistricting criteria alone (like compactness) were statistically unlikely to produce such a GOP-leaning map.
Most importantly, this lawsuit is relying on state constitutional protections for voters based on freedom of association and equal protection. While these tests have yet to persuade the U.S. Supreme Court to strike down partisan gerrymanders for violating the federal constitution, it has little latitude to override the state court’s interpretation of Pennsylvania’s constitution in this matter. Democrats gained a crucial majority on Pennsylvania's Supreme Court in 2015, and while that's no guarantee of victory, it gives the Keystone State a strong chance of a favorable ruling against GOP gerrymandering in 2018 that could produce major Democratic gains.