For more than a quarter century, two legislative districts in North Carolina have been ground zero in a fight over race and redistricting. In the course of that time, Republicans have taken control of the state Legislature, and the two political parties have reversed their legal positions regarding the use of race and drawing district lines.

When these two congressional districts first came before the U.S. Supreme Court in 1993, the court majority characterized District 12 as "bizarre," "unexplainable on grounds other than race" and bearing an "uncomfortable resemblance to political apartheid." Thereafter, the lines for District 12 and District 1 were redrawn to include African-American voting age populations that were substantial but less than a majority.

There the lines pretty much remained until after the 2010 census, when the Republican Party, for the first time, took over the state Legislature and drew the districts such that African-Americans made up more than 50 percent of the voting age population in each.

Suddenly the Democrats and Republicans flipped positions, with the GOP now arguing for districts with even heavier concentrations of black voters, and Democrats contending that such concentrations stereotype African-Americans and discriminate against them on the basis of race.

On Monday, this case and one from Virginia come before the eight justices of the Supreme Court, presenting the challenge of finding a delicate balance in considering race when drawing political boundaries — and the court's reluctance to weigh in on partisan politics.

The North Carolina case comes from a group of voters who went to court challenging the state's first and 12th districts. They contend that the Legislature packed more minority voters into these two districts in an effort to dilute their voting strength in neighboring districts.

The state defends the lines drawn for one of the challenged districts by saying it was trying to meet the requirements of the Voting Rights Act that minority voters have the chance to elect their chosen representatives. It defends the other as based on the goal of increasing a partisan advantage, not on race.

So far at least, the Supreme Court has ruled consistently that race may not be the predominant factor in redistricting except in narrow circumstances. But the court has refused to get involved in partisan gerrymandering.

"If your claim is 'we were just exercising naked political power,' well, the courts are not touching that, at least not yet," observes Richard Hasen, an election law specialist at the University of California, Irvine. "But if the claim is about race, then the courts are going to get involved."

The distinction is often "nonsensical," he says, especially in places in the South, for instance, where the vast majority of African-Americans are Democratic voters, the majority of whites vote Republican, and the overlap between race and party is enormous.

Finding the sweet spot between the Voting Rights Act requirement that minority voters have an equal chance at electing their candidates of choice while at the same time not discriminating too much on the basis of race — that's a tough order.

Stanford law professor Nathaniel Persily by his own count drew about 10 percent of legislative districts in the country following the last census. "What the court needs to figure out," he says, is how to give directions to jurisdictions that indicate "when they're allowed to take race into account" and when taking race into account will "break the Constitution."

"There is a sort of Goldilocks principle at work," he notes, meaning the states have to get the balance "just right."

"You have to have some sympathy for the jurisdictions here," he adds. "On the one hand, they know they're going to get sued no matter what they do, and yet at the same time, they know that these redistricting plans are motivated by the incumbents in order to screw their opponents."

Earlier this year, a three-judge federal court in North Carolina ruled that the two districts were unconstitutionally drawn based on race.

In a separate case from Virginia, also to be argued Monday, the districts were upheld by the lower court.

The stakes in these cases go well beyond North Carolina and Virginia, as NYU law professor Richard Pildes notes.

"The larger stakes for American democracy as well as American law," Pildes observes, are to what extent it is "required to concentrate African-Americans in election districts, and to what extent ... the Constitution actually prohibit[s] excessive concentration of African-American voters in districts."

That is in the short run, but the rules could conceivably change again after the 2020 census if the justices decide that the Constitution prohibits some level of extreme partisanship in drawing district lines. Most observers think that is a long shot, especially since the election of Donald Trump all but guarantees a continued 5-4 conservative Supreme Court majority. But Justice Anthony Kennedy, the fifth vote in that majority, has not ruled out some intervention against extreme gerrymandering.

And already there are cases posing that question headed to the Supreme Court from several other states.

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