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A DOZEN Pennsylvania state lawmakers have threatened to impeach about half of the state’s Supreme Court, after the judges quashed a heavily gerrymandered voting map that had all but guaranteed Republicans a lock on the state’s representation in Washington. The state Supreme Court’s Republican chief judge and the GOP state House’s majority leader rebuked the threat, and with good reason. Even if they do not succeed, movements to impeach state judges corrode the independence of the judiciary, and they are becoming more common.

The Pennsylvania Supreme Court had good reason to act. Gerrymandering has become a near- ­intractable crisis. In states such as Maryland, where one party uses its tight grip on the legislature to ram through highly tilted maps, reform is near-impossible. Though Pennsylvania is a purple state, it lacks a ballot-initiative system that can bypass the legislature, the maneuver citizens in states such as California have employed to introduce nonpartisan redistricting committees. As technological tools have made gerrymandering far more sophisticated, courtrooms are in many states the last forum for addressing the outrageously unfair electoral maps that result.

The partisan GOP map the Pennsylvania court threw out rewarded Republicans with a 13-5 split in the state’s congressional delegation, despite a Democratic voter registration edge in the state and narrow splits between the two parties in statewide voting. The judges gave lawmakers a chance to draw fairer lines, but the legislature failed to do so. The map the court imposed is not a Democrat’s dream, still giving Republicans a 10-8 edge.

Yet the specifics of the line-drawing miss the bigger point. Once lawmakers start punishing judges for rulings politicians dislike, the country will move closer to the full politicization of the judiciary. Pennsylvania Republicans angry now should consider how they would feel if and when Democrats threatened judges who strike down gun laws or uphold abortion restrictions. All sides eventually lose when the notion of fair judicial redress is surrendered to partisan passions.

Nationwide, state judicial impeachment and removal has been extremely rare. According to the National Constitution Center, the last instance occurred in 1994, when Pennsylvania lawmakers removed the state’s supreme chief judge “for meeting privately with an attorney to decide the outcomes of cases.” Even so, the center notes, “In recent years, there has been a trend for state lawmakers to threaten to impeach state judges for a variety of reasons.” Even threats carry a risk of pressuring judges, or appearing to pressure judges, into changing their behavior.

Philadelphia Daily News columnist John Baer raised the possibility that, instead of impeachment, the GOP legislature might reform the state courts. Ideally, lawmakers would end judicial elections and move to an appointment system, like the one that exists for federal jurists. While the motivations — reacting to a specific court decision that Republicans disliked — might be tainted, the result would be reasonable. Judges should not be elected officials, their decisions constantly scrutinized for partisan bias or favoritism toward campaign donors. Though it can stand on its own merits, the Pennsylvania Supreme Court’s ruling in the gerrymandering case would have enjoyed a greater presumption of legitimacy if it had come from judges more insulated from politics.