— Arguments wrapped Thursday in a North Carolina lawsuit that aims to change American politics.

The case targets partisan gerrymandering in general and North Carolina's current congressional map in particular. Republican legislators, attorneys for good-government groups argue, drew intensely partisan lines, using detailed data from past elections to produce maps nearly guaranteed to elect 10 Republicans and three Democrats to Congress.

Such partisan efforts have long been accepted, but the federal courts may eventually draw a line in the sand. North Carolina's case is before a three-judge panel and could take months, or even years, to run its course. A similar case out of Wisconsin has already been argued before the U.S. Supreme Court, and the court's decision is pending.

A number of other cases have delved into this issue without consensus emerging on whether the judiciary should rein in partisan redistricting, a job the Constitution delegates to state legislatures. If the courts should step in, judges must ponder, is there a consistent way to prove an unfair partisan gerrymander has occurred?

U.S. District Judge William L. Osteen Jr., head of the judicial panel in the case, seemed to search for a path forward Thursday, probing attorneys for a test.

"Everybody talks about, 'Maybe this is a constitutional problem,'" the George W. Bush appointee said, referring to past judicial opinions. "But we can't find a standard."

Much of the back-and-forth centered on a measure called the efficiency gap, which counts the number of "wasted" votes in a given district. It's a mathematical attempt to quantify the "packing" and "cracking" that goes on when legislative majorities dilute their opponents' power by stuffing as many voters of a particular party into one district as they can in order to create safe districts nearby for their own candidates.

The same concept has been at issue in separate successful lawsuits to overturn North Carolina congressional and legislative districts on the basis of racial gerrymanders.

Attorneys for North Carolina's legislative majority argue that redistricting is a political process and the domain of legislatures, not activist judges. They note that the efficiency gap measurement doesn't always work, as one of the plaintiff's experts testified earlier in the four-day trial.

If people don't like partisan redistricting, they can do something about it on election day, attorney Phil Strach said Thursday. In fact, the current Republican majority came to power in 2010, winning a wave election despite maps drawn by Democrats to favor Democrats.

"People took matters into their own hands, and we believe that's the remedy for this," Strach said.

But Republicans quickly locked in those gains, drawing new legislative and congressional maps, a process required every 10 years after the census. Anita Earls, representing the League of Women Voters of North Carolina in the case, said the state's congressional map had the worst efficiency gap score in the country last year.

For Democrats to overcome, it would take a wave election the likes of which hasn't been seen since 1972, she said.

This case is actually two lawsuits that were combined, one filed by the League of Women Voters and the other by Common Cause. Both have the same end, but their legal arguments differ.

The LWV argues for a three-prong test to prove an unconstitutional partisan gerrymander, triggered by a poor score on the efficiency gap. If that measurement points to a problem, plaintiffs must also prove partisan intent to challenge maps, Earls said. The map's effect must be "large and durable," affecting a number of districts and likely to linger for multiple election cycles, she said.

Also, map makers have to lack a legitimate reason, other than partisanship, for drawing the map as they did, Earls said.

Common Cause argues that any gerrymander meant to dilute the votes of people in a particular party should be illegal, whether it's large or small. The First Amendment and other sections of the Constitution that these arguments rely upon don't make distinctions once that sort of line has been crossed, attorney Emmet Bondurant argued.

The Constitution doesn't say, "It's OK to rig elections a little bit,'" Bondurant said.

Osteen asked how that would work in practice. The burden, Bondurant said, would be on map makers to prove they didn't abuse the copious amounts of past election data that can be used to draw maps and create safe districts.

"It's not purely a question of numbers," he said. "It's a question of why the lines were drawn the way they were drawn."

Bondurant argued, as others have, that packed and safe districts make general elections meaningless, limiting competition to primary elections and polluting American politics. They also, he said, rob one class of voters of their voice.

"If you relegate, based on political belief ... that is classic viewpoint discrimination," he said.

Strach, who is married to the state's director of elections, said repeatedly during Thursday's closing arguments that there is simply no trustworthy standard to judge partisan gerrymanders. The efficiency gap, he said, would not have caught North Carolina's infamous 12th Congressional District, which was drawn in the 1990s as a snake-like shape running down Interstate 85 and taking in population from Charlotte to Greensboro.

"If a map that mangled is not caught ... people in this country are going to have a problem with that," he said.

Osteen agreed the task of identifying gerrymanders would be difficult. But that does not mean, he said, that we should not try.

Osteen is joined on this case by 4th U.S. Circuit Court of Appeals Judge James Wynn, an Obama appointee, and U.S. District Judge W. Earl Britt, who was appointed by President Jimmy Carter. They gave no timetable Thursday for their decision in this case but gave the various sides two weeks to file post-argument briefs.