THE SUPREME COURT'S term has only just begun, but the justices have already heard arguments in what may be their most important case this year. At stake in Gill v. Whitford is whether the court will intervene against the increasingly sophisticated practice of partisan gerrymandering, in which politicians redraw the lines of legislative districts to cement their hold on power.

The high court has long been reluctant to decide when politicized mapmaking becomes so extreme as to be constitutionally unacceptable. But during oral arguments in early October, Justice Anthony M. Kennedy hinted at a possible willingness to join with the court's four liberal jurists in striking down Wisconsin's state legislative map, which the map's challengers argue was gerrymandered to entrench the Republican Party's hold on the Wisconsin legislature. The state GOP produced districts that allowed it to win a supermajority in the state assembly even after losing the popular vote in 2012, and to build further on that majority after eking out only narrow wins in the two subsequent elections.

There's nothing new about gerrymandering, which dates to the earliest days of the republic. What is new is the development of computer modeling that has transformed partisan chicanery into a precise science. The practice arguably violates constitutional principles of equal protection and free expression by punishing supporters of the minority party for their political affiliation.

Chief Justice John G. Roberts Jr. voiced concern that a constitutional standard against extreme gerrymandering would embroil the judiciary in partisan politics. In his view, the metrics used by the plaintiffs to measure the distortion of Wisconsin's districts are so much "sociological gobbledygook." It's true that no one statistical measure is perfect. But the plaintiffs put forward several methods for gauging the extent of partisan mapmaking, all of which show extreme distortion within Wisconsin. Other mathematical tests that account for natural divisions of political geography, such as the tendency of Democrats to cluster in cities, demonstrate the distortion, as well.

The chief justice's worries about the effects of an overly partisan court cut the other way, too. If the court declines to strike down Wisconsin's map, it risks undermining its own credibility by signaling to the public that the conservative-leaning justices chose to side with Wisconsin Republicans. And as attorney Paul Smith argued for the plaintiffs, the real danger of allowing partisan gerrymandering to go unchecked is the harm it does to faith in democracy as a whole. If one particular party will always win a majority of seats, what point is there in voting?

A ruling against Wisconsin would warn politicians against pushing their luck with overly partisan redistricting, even if the judiciary chooses to intervene only in extreme cases. If lawmakers don't want to risk a legal challenge, they can take the welcome step of removing redistricting from politics by creating state-level independent commissions such as those many states already use. The Supreme Court can't do all the work of restoring confidence in the democratic process, but it should not shirk the responsibility it does have.