THE 2010 elections gave Republicans unified control over Wisconsin for the first time in 12 years. Voters chose them resoundingly; when they took office in early 2011, they set out to return the favour. Armed with census data, Republican lawmakers drew districts to maximise their political advantage. In the 2012 elections, Republicans won 48.6% of the vote but took 60 of the state assembly’s 99 seats. In 2014 and 2016, their 52% of the vote got them 63 and 64 seats.

Some Wisconsinites decided this crossed the line from routine partisan activity to something more sinister. They sued the state, arguing that its partisan gerrymander was so extreme that it violated their First Amendment rights to association and free speech and the “one person, one vote” principle enshrined in the Fourteenth Amendment’s equal-protection clause. A federal district court upheld their case in a divided ruling; the state appealed to the United States Supreme Court, which heard arguments on October 3rd.

Gerrymandering is hardly new: the name dates back to an unwieldy district created in 1812 by Elbridge Gerry, then governor of Massachusetts. In most states, the legislature controls redistricting. Six states use independent commissions, and limit or bar elected officials, legislative staff or lobbyists from serving on them. Unsurprisingly, these states seem to draw more competitive districts. Elsewhere, new software and reams of voter data now allow politicians to draw surgically precise maps, while increasing polarisation has upped the stakes. As the plaintiff’s lawyer quipped, “Gerrymanders now are not your father’s gerrymander.”

Contemporary gerrymanders can compound Democrats’ geography-driven disadvantages. Democrats tend to live clustered in cities, while Republicans sprawl across more heterogenous districts. This probably contributes more to polarisation than gerrymandering does. Jowei Chen, a political scientist at the University of Michigan, has found that in many states, even without intentional gerrymandering, Democrats would still win fewer than 50% of seats with 50% of the vote. But he also found that Wisconsin’s map gerrymandered far beyond expectations. Nor is Wisconsin the only state where Republicans drew grossly contorted maps. In Pennsylvania five years ago, Republicans won 13 of 18 House seats with just 49% of the statewide vote. North Carolina’s map gives Republicans ten seats and Democrats three, despite close statewide votes. When asked why, a Republican lawmaker who headed the redistricting process said, “Because I do not believe it’s possible to draw a map with 11 Republicans and two Democrats.” And in Maryland, Republicans claim the state’s Democratic legislature gerrymandered their rights away in the rural sixth congressional district. Voters in all three states have challenged the maps in court. Wisconsin’s case is unusual because it could result in a ruling that applies nationwide. At the Supreme Court, both sides aimed their arguments—as so often happens these days—at Anthony Kennedy, the perpetual swing vote, poised between a quartet of liberals, who are probably more eager to invalidate Wisconsin’s map than the court’s four conservative justices are. In Vieth v Jubelirer, a gerrymandering case from 2004, four justices rejected the notion that courts were equipped to monitor partisan gerrymandering at all. Four others floated a quartet of standards to do just that. Mr Kennedy, as usual, split the difference. None of the standards offered avoided “substantial intrusion into the nation’s political life”, he wrote in a concurrence. But curbs on gerrymandering may be imposed “if some limited and precise rationale” one day emerges. The plaintiffs claim that day has arrived. “Social-science tools now allow courts to diagnose partisan gerrymanders with accuracy and precision,” according to a brief from two political scientists who have helped draw district maps. At issue is “partisan symmetry”—the intuitive notion that political parties should derive roughly the same legislative representation from equivalent popular support.

One way to measure symmetry, or its absence, is through the “efficiency gap”, a measure developed by Eric McGhee, a political scientist, and Nicholas Stephanopoulous, a law professor. This deems every vote cast for a losing candidate, as well as votes cast for a winner in excess of what he needs to win, to be wasted. A partisan gerrymander tries to maximise the opponent’s wasted votes by “packing” and “cracking”—creating a few safe districts that they win overwhelmingly, while spreading the rest of their voters as thinly as possible. Adding up all a party’s wasted votes, and dividing that sum by the total number of votes cast, yields an efficiency gap. An efficiency gap larger than 7% may show that one party holds an unconstitutional “systemic advantage” over the other.

Between the 1970s and 1990s, Wisconsin’s state-assembly maps averaged an efficiency gap of 1.5% in Republicans’ favour. In the three elections since 2010, that figure rose to 12.3%—meaning that winning half the popular vote would have given Republicans more than 60% of the seats in Wisconsin’s state assembly.

The conservative judges seemed unimpressed. John Roberts, the chief justice, hoarily dismissed this maths as “sociological gobbledygook”. Samuel Alito also sneered, suggesting that a single paper by a “young researcher” hardly provides an adequate basis for the justices to meddle in elections across the country. And Neil Gorsuch, the newest justice, used a hokey riff on his steak seasoning to deride the plaintiffs’ approach as “a pinch of this, a pinch of that”, with too little guidance for how to apply the test in practice. Mr Kennedy did not join his colleagues’ attack on the social sciences. Earlier in the hearing he asked Wisconsin’s lawyers a series of critical questions, which might indicate that he favours the plaintiffs.

Runnin’ down a dream

The court now faces an unenviable decision. Letting the map stand could, as the plaintiff’s lawyer warned, give states “a free pass” to create maps that, in effect, “nullify democracy”. But intervening could, as Mr Roberts fears, push the court directly into the political fray, risking what he described as “serious harm to the status and integrity” of his court.

Of course, the court could always rule on narrower grounds, as it often prefers to do. It could find that the appellants lack standing to sue, or rule that Wisconsin’s map was uniquely awful, but abstain from deciding a universal standard. Usually it prefers leaving political questions to voters. If only elected officials showed such concern for the popular will.