IN OCTOBER, the Supreme Court heard arguments over whether it should limit politicians from tinkering with legislative district lines to advantage their own party. Partisan gerrymandering has become both increasingly sophisticated and increasingly anti-democratic, as parties cement their hold on power at the cost of public faith in representative government. The court's decision to consider Wisconsin's skewed map was the first sign in years that the justices might be willing to intervene. Now, the court has taken on a second challenge.

The Wisconsin case, Gill v. Whitford, involves a Republican effort to entrench the GOP's hold on the state legislature. With the help of sophisticated computer modeling, Republican lawmakers produced maps so distorted that the party won a supermajority in 2012 even after losing the popular vote. The newer case, Benisek v. Lamone, concerns gerrymandering by Maryland Democrats seeking to unseat a Republican member of Congress. In 2011, the state's Democratic government redrew Maryland's 6th District to shift Republican voters out and Democratic voters in. Rep. Roscoe G. Bartlett (R) lost his previously safe 6th District seat to a Democratic challenger in 2012 — a victory for what Democrats described as their "7-1 plan," named after their effort to net seven of Maryland's eight congressional districts.

It's rare for the Supreme Court to take up a second case concerning an issue it is already considering. The addition of the Maryland case may signal the court's willingness to strike down extreme gerrymanders. During oral arguments over Gill, Justice Anthony M. Kennedy appeared open to siding with the four more liberal justices against Wisconsin's map.

The two cases offer different ways for the justices to think through the problem of partisan redistricting. Maryland's challengers — current and former residents of the 6th District — focus only on their own district's reshaping. They argue that gerrymandering limits their political voice on the basis of their party affiliation, violating their free-speech rights. In Wisconsin, the plaintiffs take aim at the redistricting of the entire state in favor of Republicans. They make the case that this unbalanced political influence along party lines goes against the Constitution's promise of equal protection, as well as freedom of speech.

The Supreme Court has hesitated to tackle partisan gerrymandering for fear of entangling itself in partisan politics. But Maryland and Wisconsin show that gerrymandering is an issue of bipartisan concern. The contest is not Republicans vs. Democrats, but political parties seeking an unbreakable hold on power vs. voters who just want representation.

The justices should take this chance to set standards against extreme partisan gerrymandering. Where to draw the line between acceptable and unacceptable gerrymanders is a delicate question, and the courts will not want to involve themselves in every electoral dispute. But making clear that there's a limit to constitutionally acceptable gerrymandering would deter lawmakers from chicanery going forward. It should also encourage them to hand the redistricting process to independent, nonpartisan commissions — the ultimate solution to this problem.