Racial gerrymanders have been undone many times, most recently when the Supreme Court ruled against a pair of North Carolina congressional districts this week. But another case from that same state, heading into federal court next month, has a shot at eventually persuading the justices to do what they’ve never done before: strike down an election map as an unconstitutionally partisan gerrymander.

The high court ruled three decades ago that it may be unconstitutional to draw political boundaries so that one party was sure to win a disproportionate number of elections, but it’s never come up with a means for deciding when such mapmaking has become too extreme.

The new lawsuit involving North Carolina congressional districts stands to provide just such a rationale. That’s especially true if it ends up getting paired with a similar case involving Wisconsin’s state legislature districts, which the Supreme Court seems virtually certain to consider in its term beginning this fall.

Plaintiffs in both cases say the maps tilt election outcomes so much in favor of Republicans as to violate Democratic voters’ rights of free expression and equal protection. And they have united behind a pretty straightforward mathematical formula for illustrating how that’s so.

It’s a standard that, if adopted, would give the courts a method for deciding whether partisan gerrymandering has become excessive not only in the Wisconsin and North Carolina cases, but also during the nationwide surge of political cartography that will get started right after the 2020 census.

That would probably not be good news for Republicans. They hold dominance in the state capitals and are counting on the legal status quo to help them maintain, if not expand, their power in many of the biggest states — where their legislative throw-weight during this decade has far exceeded their routine share of the vote. 

‘The efficiency gap’

The bottom line of the equation in question has been dubbed “the efficiency gap” by its inventors, Nicholas Stephanopoulos of the University of Chicago Law School and Eric McGhee of the Public Policy Institute of California. They say their aim is calculating the number of “wasted votes” in a state’s elections and then measuring the difference between how many votes Republicans and Democrats have squandered.

They define wasted ballots as those that don’t help a party’s candidate to victory. This happens as a consequence of both techniques at the disposal of partisan mapmakers, known as cracking and packing.

If Democrats draw the lines and “crack,” or spread, the Republican voting base among so many districts that the party lacks a viable majority in any place, then the GOP ends up wasting all the ballots cast in the races where they’re defeated — no matter how narrowly.

If the Republicans “pack” as many Democrats as they can into a district or two, with the aim of helping the GOP win everywhere else, then the Democrats end up wasting all the ballots cast beyond the bare minimum required to elect their few candidates.

The difference between the two parties’ wasted votes, divided by the total number of ballots cast, is the efficiency gap. Under a map drawn without any partisan bias, Democrats and Republicans will waste about the same number of votes and the efficiency gap is going to be close to zero. The more one party gerrymanders the other toward electoral oblivion, the wider the gap grows.

How big a gap violates the Constitution? Assuming the courts agree to apply the efficiency gap standard, or even consider it, the lawyers from the two states arguing in favor of the formula are contemplating somewhat different ways of answering.

Power play

The Wisconsin case is about what happened after the GOP won control of all the levers of power in Madison, just in time for this decade’s redistricting, and drew a state House map that resulted in Republicans winning 60 of the 99 seats in 2012 even though they won only 49 percent of the statewide legislative vote. Two years later, the GOP won 63 seats with 52 percent of the total vote.

Those numbers yielded efficiency gaps of 13 percent in 2012 and 10 percent in 2014. And those figures were used by the lawyers who last November persuaded a panel of three federal judges to strike down the map, ruling it “was designed to make it more difficult for Democrats, compared to Republicans, to translate their votes into seats.”

The plaintiffs argued that a gap exceeding 7 percent, sustained over several elections, is unconstitutional. The judges didn’t base their ruling on that argument, but it’s bound to be resurrected before the Supreme Court by those arguing for and against Wisconsin’s map. (Some cases about elections take a direct path to the high court, and this is one of them.)

The North Carolina case is the latest in a state that’s seen its congressional map under almost perpetual court scrutiny for decades. Before now, the legal challenges have always focused on minority voting power, with the Supreme Court ruling Monday that the districts represented by the two African-American Democrats in the House delegation, Alma Adams and G.K. Butterfield, were unconstitutional racial gerrymanders designed to concentrate as many black voters in as few places as possible in order to diminish their political strength elsewhere.

Now the state’s lawyers, in a trial set to begin June 26, will have to defend the mapmakers in the Republican-majority General Assembly from a very different allegation: that their motivation for drawing the statewide congressional map was unconstitutionally partisan, effectively abandoning the court’s “one person, one vote” standard for districts (a breach of the 14th Amendment) and punishing a group of people because of their political beliefs (in violation of the First Amendment).

As in Wisconsin, the GOP took over at the state capital in time for this decade’s redistricting, and their cartography soon remade the House delegation’s balance of power. Four elections ago, Democrats won seven of the 13 seats. Last year, they won only three, even though their candidates took 47 percent of the congressional vote statewide.

And that 10-3 distribution was precisely the aim of the GOP state legislators, their redistricting point man state Rep. David Lewis has declared, only “because I do not believe it’s possible to draw a map with 11 Republicans and two Democrats.”

The plaintiffs, led by Common Cause and the League of Women Voters of North Carolina, are using a different formulation Stephanopoulos has come up with to illustrate how the efficiency gap can result in the racial gerrymandering of congressional maps — what he calculates as the “two-seat threshold,” meaning one party has a reliable hold on at least two more seats than it would if the efficiency gap were closer to zero.

Measuring the cost

By Stephanopoulos’ reckoning, six states other than North Carolina are currently electing House members using maps that meet or exceed the two-seat threshold, all in favor of the GOP: Florida, Texas, Ohio, Pennsylvania, Michigan and Virginia.

After crunching the data, another academic, Princeton professor Samuel Wang, concluded that political gerrymandering had cost Democrats as many as 22 House seats in 2012, and winning all of them would have given the party a narrow majority.

In legislative elections in 2012 and 2014, according to another study by Stanford political scientist Simon Jackson, there were efficiency gaps above 10 percent in favor of the Democrats in just two states, New York and Rhode Island, but of that magnitude in favor of the GOP in 10 states: Florida, Indiana, Kansas, Michigan, Missouri, North Carolina, Ohio, Virginia, Wisconsin and Wyoming.

The Republican National Committee has already filed a brief asking the Supreme Court to decide against any application of the efficiency gap, deriding it as “a tool that advances the partisan interests of the Democratic Party.” The national GOP and others say the disconnect between statewide vote percentages and share of House seats results not from bias but from demographics — the reality that Democrats concentrate in the big cities, allowing the GOP to win so many elections in the suburbs and rural areas.

As with so many other high-profile cases at the Supreme Court, Justice Anthony M. Kennedy is destined to be a pivotal voice if a map ever gets struck down as a partisan gerrymander — either because it fails an efficiency gap test or some other standard.

Kennedy set himself up as a future swing vote in an important 2004 case. He joined four colleagues for a majority reiterating that political motives in mapmaking could theoretically go too far, but then he joined his other four colleagues to form a majority upholding the map in question, which GOP legislators had drawn with the stated purpose of guaranteeing that most congressional districts in a “bluish purple” Pennsylvania would nonetheless be reliably “red” for a decade.

“Courts must be cautious about adopting a standard that turns on whether the partisan interests in the redistricting process were excessive,” he wrote somewhat elliptically. “Excessiveness is not easily determined.”