Expert witnesses have finished tangling, at least for the moment, in the North Carolina redistricting dispute. After a narrow majority of the Supreme Court refused to impose constitutional barriers to partisan redistricting, federal challenges to political gerrymandering in North Carolina became impossible to pursue.

Challengers are now basing their claims on the state constitution, a strategy that put an end to partisan gerrymandering in Pennsylvania. The U.S. Supreme Court noted that state courts applying state laws and constitutions have the power to address political gerrymandering, even if federal courts do not.

On the other hand, the Supreme Court has long recognized that redistricting schemes may not disenfranchise nonwhite voters. Evidence that a map-drawing expert may have done just that could lead to a renewed federal challenge to North Carolina’s redistricting, even if the state challenge does not succeed.

Constitutional Challenges to Gerrymandering

In a 5-4 decision reflecting the ideological division of the Supreme Court, the majority ruled that partisan gerrymandering — drawing congressional districts in a way that favors one political party, diminishing the voting power of voters for the opposing party — is not a constitutional violation that federal courts are capable of remedying. “That’s politics” is a shortened version of the majority’s decision.

The fact that Republican legislators in North Carolina drew districts during the 2010 redistricting to favor Republicans is readily (even proudly) acknowledged by some Republican state legislators. Democrats did the same thing when they drew maps during the 1990 and 2000 redistricting. Courts struck down many of the maps drawn by Democrats and did the same to the Republican map. In those cases, the maps were invalidated as racial gerrymandering.

The Republican-controlled legislature redrew the maps again in 2016, supposedly to eliminate racial gerrymandering. Candidates from the Republican and Democratic parties received almost an equal number of votes in the 2018 congressional elections, but Republicans were elected to Congress in 10 of the state’s 13 districts. Gerrymandering is the only reasonable explanation for that result.

The North Carolina Democratic Party and Common Cause are now challenging partisan redistricting in state court. They argue that the free speech and association protections of the state constitution are violated by a redistricting process that deliberately gives disproportionate representation to one political party.

Expert Testimony

Several experts have testified in the state court trial. The 2016 maps were drawn by recently deceased mapmaker Thomas Hofeller. Expert witness Wesley Pegden, using mathematical algorithms, drew millions of maps of districts that were contiguous and roughly equal in population — the standards required by state law. He testified that none of those maps, drawn at random, gave Republicans the same advantage as Hofeller’s maps.

Pedgen, an associate professor in Carnegie Mellon University’s department of mathematical sciences, concluded that the maps were deliberately drawn to favor Republicans. A court in Pennsylvania accepted his methodology and conclusions when it struck down a partisan gerrymander in that state.

Other expert witnesses, including Christopher Cooper, a professor at Western Carolina University, arrived at the same result. After he was given access to Hoffler’s files, Cooper discovered that lines had been carefully drawn to move Democratic Party voters into districts that were safely held by Republican representatives. He concluded that Hofeller deliberately attempted to dilute the voting power of Democrats.

Exclusion of Expert Testimony

Hofeller’s daughter made his files available to the challengers after his death. While the Republican legislators claimed that the files were not the daughter’s to give, the court ruled that at least some of the data in the files could be admitted as evidence.

The challengers contend that Hofeller secretly and improperly used racial data to help him draw the maps that the legislature enacted, a practice that has long been forbidden. The Republican legislators contend that Hofeller drew maps of his own as a hobby and that he did not use racial data in drawing the maps he presented to the legislature.

After reviewing the files, expert witnesses for the challengers concluded that Hofeller relied on racial data to complete the maps before the legislature created rules that prohibited him from considering race. To counter that testimony, the Republican legislators called political scientist Douglas Johnson as an expert witness.

Johnson testified that Hofeller’s “personal maps” were dissimilar to the maps the legislature actually approved. On cross-examination, however, Johnson admitted that his analysis failed to consider eleven districts on the “personal maps” with boundaries nearly identical to those of districts approved by the legislature.

Johnson also admitted that his analysis relied on unweighted population calculations that should have been weighted. That error compounded the unreliability of his statistical analysis.

The Republican leader of the North Carolina Senate had claimed that Hofeller’s “personal maps” more closely resembled maps that Common Cause proposed as fair in 2017 than maps that the legislature enacted. Johnson admitted that he provided that opinion to the senate leader and that he probably owed the senate leader an apology for doing so.

Applying a Daubert analysis, the court concluded that Johnson did not base his opinion on reliable data or a reliable methodology. Johnson essentially cherry-picked data to support the conclusion he wanted to reach. The court therefore decided it would not consider Johnson’s unreliable conclusions.

Trial Concludes

Another expert for the Republican legislators, Thomas Brunell, testified that partisan gerrymandering is an accepted outcome of the political process. He opined that the map adopted by the legislature was not outside the norms of redistricting.

Having heard all the expert evidence, the three-judge panel will likely render a decision in the coming months. The dispute is unlikely to end quickly, however, as the party that loses is almost certain to appeal.