A math department's take-down of gerrymandering in North Carolina

We are in the lull between two important legal arguments that could determine whether voters will be allowed choose the politicians who represent them, or politicians can continue to select the people who elect them.

Both cases are remarkable — not just because of the constitutional questions involved, but because of the prominent new players they’re bringing into a highly politicized debate.


Last week, the U.S. Supreme Court heard a challenge to the district maps drawn for the lower chamber of Wisconsin’s state legislature in 2011. The next year, Republicans won 48.6 percent of the statewide vote, but 60 of 99 assembly seats.

Next week, a panel of three federal judges in North Carolina will hear a challenge to that state’s congressional districts. Again, the statewide vote is closely divided – a Democrat narrowly ousted a sitting Republican governor in 2016. But at the same time, the GOP won 10 of 13 congressional districts.

Last week or next week, the basic questions are the same: Is there a point at which partisan gerrymandering becomes unconstitutional? Is there a limit to the ability of one political party to place voters in certain boxes to ensure it stays in power?

The answers will be closely examined here. They could determine how far, in the next decade or so, Georgia Republicans will be allowed to go in any effort to maintain their edge in the face of a rapidly changing voting population.

Both cases have something else in common: The Duke University mathematics department.

In the Wisconsin case, a September research paper published by department chair Jonathan Mattingly and his colleagues found “robust evidence that the district maps are highly gerrymandered.” The paper served as the basis of an amicus brief in the case.

Mattingly and other number-oriented savants will give direct testimony in next week’s North Carolina case. The Duke University mathematics department is, in a sense, the inspiration for the legal challenge. The state’s political boundaries have been a topic of study by Duke faculty and students for the last four years.

There is a reason we’ve come to this. Over the last few decades, the redistricting that occurs every 10 years after every census has become the domain of computers. Agendas can be subtle and hard to detect. Discovering those agendas requires more and more sophistication.

“I grew up in North Carolina,” said Mattingly in a telephone interview. “I know a lot about the state. We believe in regional government. We believe in regional representation, and the people aren’t homogeneously mixed.”

Republicans took control of the state legislature in 2010. New maps were drawn in 2011, and the disparities between the statewide vote and district results began showing up in 2012.

“So I asked myself and my students, could you look at this and decide what the right answer should have been?” said Mattingly, a professor of mathematics and statistical science.

“We want to identify what the background signal is. What’s typical, and what’s anomalous. What seems to be okay, and what needs to be defended,” the mathematician said.

Mattingly denies partisanship, and says his team has also identified efforts by Democrats in Maryland to freeze out their Republican rivals.

The tools they use are complicated. Personally, I fade out shortly after reading this line from a May study of North Carolina congressional districts published by Mattingly and his team: “Using a Monte Carlo algorithm, we randomly generate over 24,000 redistrictings that are non-partisan and adhere to criteria from proposed legislation.”

For us simpletons: Suppose you have a sack, and you stuff that sack with 24,000 different versions of congressional maps – all using the same voting results of the 2016 election.

If you reach into the sack, what are you most likely to pull out? The answer: A North Carolina map in which Democrats win five, six, seven – or even nine of the state’s 13 congressional districts.

Only in very rare circumstances would you pull out a map that gives Democrats only three seats. Mattingly and his crew call that evidence of a “highly engineered” result. And it worries him.

“There’s a simple question of democracy here,” Mattingly said. “If you can change between three and nine Democrats elected by messing with the districts, how can we even pretend that we’re listening to the democratic signal, right? The will of the people – you can’t hear it through that.”

“The most important thing is who drew your maps, not who voted,” the mathematician said.

Because the math is rather high-toned, there is the danger that it can be easily dismissed. “Sociological gobbledygook,” was the phrase used by John Roberts, the chief justice of the U.S. Supreme Court, during last week’s argument over the Wisconsin case.

But in the North Carolina case, the mathematicians and probability experts will only be certifying what the GOP authors of the map have already admitted to.

In 2016, a federal court threw out the congressional map that state GOP lawmakers had drawn, declaring that two districts had been gerrymandered to reduce the voting strength of African-Americans.

The North Carolina legislature quickly produced a substitute that was the basis for last year’s elections. Instead of using race, lawmakers openly used voting results for Democratic or Republican candidates in past statewide elections.

“We want to make clear that we…are going to use political data in drawing this map. It is to gain partisan advantage on the map,” one GOP lawmaker publicly stated. “I want that criteria to be clearly stated and understood.”

The same lawmaker said he proposed a congressional map drawn to produce 10 Republicans and three Democrats “because I do not believe it’s possible to draw a map with 11 Republicans and two Democrats.”

So the question to be posed is relatively clear.

Next week’s challenge to the 2016 North Carolina map is the result of two lawsuits that have been merged together.

Ben Thorpe, an attorney with the Bondurant, Mixson & Elmore law firm of Atlanta, is representing Common Cause, one of several parties in the action. “When the other court dismissed the first map on the basis of race, [North Carolina lawmakers] thought the answer to that was to say that it was all about party," he said. "That sets up the legal test as squarely as you will see it.”

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About the Author

Jim Galloway
Jim Galloway
Jim Galloway is a three-decade veteran of The Atlanta Journal-Constitution who writes the Political Insider blog and column.