When Does Political Gerrymandering Cross the Line?

By Jo Craven McGinty (WSJ)

March 15, 2019 7:30 a.m. ET

With the Supreme Court set to consider political gerrymandering, a look at ways to measure the impact of redrawing election maps

I get it. Winning is better than losing. So, why wouldn’t politicians put a thumb on the scale to ensure a partisan victory?

At least once a decade, usually following the decennial census, states redraw election districts to have about the same number of people and to ensure every community has equal representation. Members of Congress, state legislators and many local officials are elected by voters who are grouped this way.

In a few states, independent commissions draw the lines. But in most, state legislatures wield the pen. In those instances, politicians may draw maps to benefit themselves and their own parties.

Recently, Maryland Democrats did. So did North Carolina Republicans. Both have ended up in court.

On March 26, the U.S. Supreme Court will hear oral arguments in the cases, with plaintiffs alleging the party controlling each state legislature deliberately created congressional districts to disadvantage voters on the other side.

While the Supreme Court has long said partisan gerrymanders are anti-democratic and unconstitutional, the justices haven’t yet come up with a test for how to bring a claim, according to Michael Li, an attorney who focuses on redistricting at New York University’s Brennan Center for Justice.

Perhaps emboldened by that lack of clarity, some politicians have pushed the envelope.

In one videotaped meeting in 2016, the chair of North Carolina’s committee on redistricting, said: “I propose that we draw the maps to give a partisan advantage to 10 Republicans and three Democrats because I do not believe it’s possible to draw a map with 11 Republicans and two Democrats.”

He got a laugh. But the legislature went on to outline districts that netted the desired split (although a new vote will be held in the Ninth District because of alleged ballot tampering).

Maryland politicians were also unabashed. In a court deposition in 2017, then-Gov. Martin O’Malley explained why the lines for a previously safe Republican district were changed: “Everybody pretty much knew that, as we redrew the lines, it would put more Democrats and Independents into the Sixth District,” he said.

The maneuver helped give his party seven of the state’s eight congressional seats.

The Supreme Court has been asked to address two things: Are there judicially manageable standards for determining when a partisan gerrymander violates the Constitution, and, if so, what are they?

There are multiple ways to test district maps for partisanship. North Carolina offers a particularly interesting set of circumstances because its statewide elections tend to be close. Democrats and Republicans split 49.7% to 49.4% in the 2008 presidential election, 48.4% to 50.4% in 2012, and 46.2% to 49.8% in 2016.

If members of a political party are grouped together naturally—a rural-urban divide between Republicans and Democrats is common—district-level election results could be lopsided, even if statewide elections aren’t.

“Might we get something like a 10-3 outcome as a function of the geography?” said Jonathan Rodden, a political scientist at Stanford and author of the book “Why Cities Lose: The Deep Roots of the Urban-Rural Political Divide.”

To find out, Jowei Chen, a political scientist at the University of Michigan who has provided expert testimony in the case, ran 1,000 computer simulations to create valid North Carolina district maps that equalize populations, minimize county splits and maximize geographic compactness—the traditional goals for drawing the maps.

The simulations generally resulted in six or seven Republican districts.

Dr. Chen then constructed maps to ensure no two incumbents would end up in the same district and have to face each other for re-election. Those simulations resulted in seven or eight Republican districts.

Finally, he tested whether any plan could adhere to the traditional goals and also guarantee Republicans 10 of 13 districts. None could. The enacted plan, Dr. Chen found, represents an extreme statistical outlier.

Simulations are one of several means that plaintiffs have used to test for the existence or impact of partisan gerrymandering. Two others are vote share and the efficiency gap.

The difference between a party’s mean and median vote share shows whether the party is “packed” into certain districts, although it doesn’t reveal whether packing is intentional.

The efficiency gap computes the portion of seats the dominant party won because it “wasted” fewer votes; wasted votes are those cast for a losing candidate plus those cast for a winner in excess of the number needed for victory. The efficiency gap is calculated by dividing the difference between the two parties’ wasted votes by the total number of votes cast.

Adopting a standard for judging district plans would represent the broadest victory for plaintiffs, according to Nicholas Stephanopoulos, a lawyer involved in the North Carolina case and a professor at the University of Chicago Law School. But it will take the Supreme Court several months to issue a ruling.

Until then, a suggestion: Why don’t Democrats and Republicans do something radical? Try convincing a majority of voters their policies are better than the other side’s. And let the votes fall where they may.

Write to Jo Craven McGinty at Jo.McGinty@wsj.com