The Supreme Court Looks at the Math of Gerrymandering

Redistricting along party lines is going to get its day in court.

U.S. Supreme Court

Photographer: Brooks Kraft/Getty Images

In 1986 the U.S. Supreme Court ruled that if legislatures draw district boundaries along party lines, they could, in theory, be in violation of the Constitution. For three decades that ruling remained  hypothetical because the court didn’t agree on standards of what qualified as unfair. That could now change. On June 19 the Supreme Court agreed to hear a new caseGill v. Whitford, that will consider the district lines of Wisconsin to determine whether there’s a way to figure out how far is too far in partisan gerrymandering.

The case springs from 2010 when, for the first time in more than 40 years, Wisconsin Republicans won control of the governorship and both houses of the state legislature. The next year, the state Republican leadership led efforts to redraw the districting maps.  The legislature adopted new district boundaries in time for the 2012 election, when Republicans won 60 of the Wisconsin State Assembly’s 99 seats, despite the fact that, in aggregate, more people voted for Democratic Assembly candidates statewide.

In 2015 voting rights attorneys sued state election officials on behalf of a dozen Democratic voters, including the lead plaintiff, Bill Whitford, an emeritus professor at the University of Wisconsin Law School. In November 2016 a three-judge federal panel ruled in favor of Whitford, finding that Wisconsin’s maps did unfairly favor the state’s Republicans. That ruling was then appealed by Wisconsin’s attorney general. It’s that appeal that the Supreme Court is agreeing to hear. 

While courts have ruled that drawing district boundaries in a way that explicitly deprives racial minorities of votes does violate the Voting Rights Act, it’s much trickier to determine whether a legislative map favors one political party over another, in part because political views can change. The Whitford team has proposed using a data-driven method called an “efficiency gap” to calculate whether districts are being drawn in a way that unfairly favors one party. To do so, the efficiency gap method tries to quantify the two main strategies for partisan redistricting: packing, where the party in charge draws boundaries that cram as many people of the opposing party as possible into a single district; and cracking, where districts are drawn in a way that divides voters of the same party across many districts so they don’t form a majority. In packed districts, the efficiency gap considers all of the votes over 50 percent—that is beyond those needed to get a candidate elected—to be superfluous, or “wasted”; and in cracked districts, all votes for the losing party are deemed wasted. 

“Even a very fair plan results in lots of wasted votes,” Nicholas Stephanopoulos, an assistant professor at the University of Chicago Law School, told Bloomberg Businessweek in 2015, when the case was headed to federal district court. Stephanopoulos, who co-authored an academic article proposing the efficiency gap methodology and is one of the lawyers on the Wisconsin case, said unfair plans lead to one party wasting way more votes than the other, and, therefore, is far less efficient in converting voters into seats. The Wisconsin gerrymander, according to the original plaintiffs, was better than 96 percent of political maps their team examined at giving one party an electoral advantage.

When the federal judges ruled in November, they cited the efficiency gap as “corroborative evidence of an aggressive partisan gerrymander.” The Campaign Legal Center, which leads the Whitford case team,  proposed it as a tool to help outline more precise standards for when partisan gerrymanders go too far. Whether the Supreme Court chooses to do so may be key to its decision. 

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