— A legal donnybrook over how North Carolina lawmakers carved the state into 13 congressional districts will give the U.S. Supreme Court a chance to weigh in on how and when race may be used in drawing political boundaries.

The court will hear oral arguments Monday in Harris v. McCrory, the case that sparked a do-over congressional primary in June. It is one of several federal cases that has rewritten the rules for North Carolina elections over the past year and could help set the rules for how legislatures here and in other states divvy voters into districts for years to come.

Such cases are high-stakes affairs because partisan control of the Congress and state legislatures can hinge on how lawmakers draw district boundaries. In this case, individual plaintiffs and progressive groups say North Carolina Republicans pushed racial preference rules to extremes in order to ensure a GOP advantage in 10 of North Carolina's 13 U.S. House districts.

"If you're going to have a racial gerrymandering standard, the North Carolina case calls out as an example of where there's a violation," said Jon Greenbaum, chief counsel and senior deputy director of the Lawyers’ Committee for Civil Rights Under Law, which filed an amicus brief in the case.

But lawyers for the state have argued that the legislature has been forced to grope for a nearly impossible-to-find Goldilocks zone between taking race into account and not overstepping an ill-defined line.

"Racial gerrymandering doctrine is substantially complicated by the reality that the Voting Rights Act has been interpreted to sometimes require states to prioritize race when drawing its districts," lawyers representing North Carolina wrote in a brief for the court.

Sen. Bob Rucho, R-Mecklenburg, one of the drafters of the contested maps, said the state followed federal voting rights laws as they were understood at the time. The three-judge panel that heard the case now on appeal, he said, changed the rules after the fact.

"Redistricting is one of the most challenging jobs in the world, especially if they don't give you the guidelines to do it," Rucho said. "We used the law the way it was written, the way it was clearly stated."

The legal concepts at play in this case are very similar to a separate case in which a federal court ordered the General Assembly to redraw its own districts and hold new elections next year. Observers on both sides of those cases expect how the justices rule in the Harris case to telegraph what they might require in that second case.

A long history of legal challenges

Although race is one factor that can be used in drawing districts, it is supposed to take a back seat to other "traditional" redistricting criteria such as keeping districts compact – rather than splayed over a wide and winding geographic area – and keeping cities and counties from being unnecessarily divided. Most importantly, each district must represent roughly the same number of people.

At the core of the North Carolina case is a push and pull between those race-neutral factors and what is required under the Voting Rights Act of 1965, which was designed to ensure that minority communities could elect the candidates of their choice.

North Carolinians have a long history of state and legal challenges to various iterations of federal, state and local political districts. One or both of the two districts at issue in the Harris case – the 1st Congressional District and the 12th Congressional District – have been the subject of Supreme Court cases five times over the past 30 years.

As it was first drawn by Democrats in the 1990s, the 12th District meandered from Charlotte to Greensboro along Interstate 85, resembling a snake that twined two major metropolitan areas as well as a thin slice of suburban and rural North Carolina. The 1st District has long been something of a jellyfish, the main portion of which floated in the northeastern part of state with tendrils that reached into various minority communities in and around the Triangle.

Republicans inherited those basic shapes when they took majorities in the state House and state Senate following the 2010 elections.

When they set about redrawing the districts, GOP legislative leaders observed that the 1st District was originally created as a "majority minority" district and said they needed to draw more black voters into the newly mapped area in order to comply with federal voting rights law. Those who challenged the district pointed out that Democratic Congressman G.K. Butterfield won election there with fewer than half the district made up of black voters.

As to the 12th District, Republicans have said their main objective was concentrating as many Democrats into the same basic area. At the same time, they also included more minorities in order to avoid charges of "retrogression," or diluting minority voting strength.

"The 12th, which is one of the ugliest ones in the nation, is one that has been litigated and litigated and litigated," said Rep. David Lewis, R-Harnett, one of the main architects of the redistricting plan. "I can tell you, as one of the map drawers, we didn't want to draw the 12th the way it was drawn. But we kept the shape – we kept the flow of the thing – because it was approved by the courts as a heavily Democratic district. That's what they had approved time and time again, so we basically left it alone."

But critics of the 2011 maps say lawmakers went beyond what was necessary to preserve the basic shape of the districts and protecting incumbents.

"They really went out of their way, and they went out of their way in terms of breaking up communities," Greenbaum said. "You have lots of examples in which they specifically broke up political units to get more black voters into the district, and they really didn't need to."

The North Carolina Supreme Court sided with Rucho, Lewis and other GOP lawmakers when a group of Democrats brought a case through the state court system. But in a February ruling, a panel of three federal judges disagreed, saying that race took a front-and-center role in the 2011 redistricting effort.

"There is strong evidence that race was the only nonnegotiable criterion and that traditional redistricting principles were subordinated to race," 4th U.S. Circuit Court of Appeals Judge Roger Gregory wrote for the court. "In fact, the overwhelming evidence in this case shows that a (black voting-age population) percentage floor, or a racial quota, was established in both CD 1 and CD 12. And, that floor could not be compromised."

Rucho said the federal judges ignored evidence in the record of "racially polarized voting," particularly in the 1st District, in order to reach its rules. He also pointed out that one member of the three-judge panel found that the snaking 12th District was constitutional. Meanwhile, he said, the judges did nothing to give lawmakers guidance on how to draw what the judges would consider legal districts.

Nevertheless, that ruling forced lawmakers to redraw the congressional districts in February, throw out the results of the March primary and hold a new congressional primary in June. That second set of districts, which is also being challenged, is at least more compact. The 12th District, for example, has shrunk from a snake down to a ball centered on Charlotte, while the 1st District has lost its tendrils.

The redrawing had an impact on some individual lawmakers – 2nd District Congresswoman Rene Ellmers lost her seat in a Republican primary showdown with 13th District Congressman George Holding after the 13th District was shifted from the Triangle to the Triad – but it did little to change the state's partisan representation. Ten Republicans and three Democrats represented the state following the 2011 plan, and 10 Republicans and three Democrats were elected to represent the state next year using the 2016 maps.

If the Supreme Court rules in favor of the state, overturning the lower court's order, North Carolina will revert to the more sprawling districts in the 2018 and 2020 elections.

Republicans will argue Monday that North Carolina should not be punished for trying to follow the rules at the time.

"When a State engages in the core sovereign task of drawing the districts that will govern its elections, and it makes a good-faith effort to comply with federal law, federal courts should not stand in judgment years later just because they believe the State may have been a bit overcautious in trying to abide by its obligation to protect the ability of a minority group to elect its candidates of choice," reads one of the state's briefs in the case.

Using race as a tool

These thorny problems land on the doorstep of a Supreme Court split evenly between four liberal and four conservative justices. The court's ninth member, Associate Justice Antonin Scalia, died early this year, and congressional Republicans blocked President Barack Obama's efforts to replace him.

If the eight justices deadlock, the lower court's ruling will stand.

"Justice Anthony Kennedy will tell us a lot about where this case goes," said Kareem Crayton, a visiting professor of law at Vanderbilt University who served as a consultant to North Carolina Democrats during the redistricting process.

Kennedy, who was appointed by President Ronald Reagan, has long been viewed as a swing vote on the court. Should five members make a firm decision, they would set a precedent likely to be respected even when a new member joins the court. A deadlock in the Harris case could pave the way for North Carolina's legislative redistricting case, known as Covington vs North Carolina, to be more decisive.

Although there has long been consensus on the court that racial gerrymandering isn't allowed, there has as yet been little agreement as to what an objective standard might be.

The North Carolina case is one of two coming before the court on Monday. A second case out of Virginia deals with legislative districts. Greenbaum said that the Virginia case is less clear that race had been an overriding factor. The contrast between the two cases, he said, could be helpful if Kennedy wants to craft a standard.

"I think these two cases actually provide an opportunity for a justice like Kennedy to define where that line is," Greenbaum said.

Crayton agreed that the North Carolina case was the more "extreme" of the two.

"I don't think there was a more ham-handed way for the Republicans to try to accomplish what they accomplished," he said. "To put it simply, I think they got greedy."

Crayton argues that race was merely a fig leaf that Republicans used to achieve partisan ends.

Rucho and Lewis both insist they did only what was required by the state of the law and prior Supreme Court decisions.

"For people who say we stacked those districts for Republicans, it is not true," Rucho insisted Friday, pointing out that Republicans are not favored by voter registration in those 10 districts like Democrats are in the 1st District, 4th District and 12th District.

While acknowledging that lawmakers examined how those districts "performed" – whom voters in them backed during prior elections – he said that past performance offered no guarantees.

Like those on the other side of the case, Rucho said he hopes the court offers lasting guidance for North Carolina and other states.

"Just tell us what's legal," he said.