RALEIGH – A new lawsuit alleges a congressional redistricting plan drawn by Republicans in Raleigh is “one of the worst partisan gerrymanders in modern American history.”

It’s not just a wild assertion made for effect. The plaintiffs say they can back it up.

The lawsuit, filed by the Southern Coalition for Social Justice and the Campaign Legal Center on behalf of the League of Women Voters of North Carolina and individual voters, offers an analysis of the districts that the plaintiffs hope the courts will see as a valid way of determining the extent of partisan gerrymandering in the future.

The U.S. Supreme Court has recognized that excessive partisan gerrymandering is unconstitutional. But recent challenges have failed because plaintiffs haven’t offered an acceptable standard to distinguish between permissible political line-drawing and unlawful partisan gerrymandering.

The analysis proposed in the case is called the “efficiency gap,” the difference between the political parties’ “wasted” votes in an election, divided by the total votes cast. Under the analysis, “wasted” votes are votes cast for a losing candidate, plus votes for a winning candidate in excess of the number needed to win.

The efficiency gap captures in a single number a redistricting plan’s “cracking and packing,” the two ways in which partisan gerrymanders are drawn. “Cracking” means dividing a party’s supporters among multiple districts so they fall short of a majority in each district. “Packing” refers to concentrating a party’s supporters in a few districts so their preferred candidates win by overwhelming margins in those districts, while diluting their influence in other areas.

Cracking and packing allow the party drawing the districts – currently Republicans in North Carolina – to manipulate vote totals in its favor.

According to the lawsuit, North Carolina’s efficiency gaps in 2012 and 2014 “exhibited pro-Republican partisan biases larger than 25 percent – by far the worst in North Carolina’s modern history and at the far edge of the nationwide distribution.”

“The Constitution guarantees everyone’s right to participate equally in an electoral system that does not discriminate against them because of their beliefs,” said Anita Earls, executive director of the Southern Coalition for Social Justice. “It’s clear that the intent and effect of creating North Carolina’s 2016 congressional maps were to manipulate the democratic process. The result disparages voters and ensures that one party can maintain political power even when a majority of the state’s voters do not support them.”

Even if Democratic candidates earn a majority of the statewide vote, the new redistricting plan would enable Republican candidates to win 10 of 13 seats, and the districts were drawn with exactly that in mind.

The suit’s plaintiffs proposed a three-prong test for partisan gerrymandering. First is “discriminatory intent.” Was the redistricting plan drawn with the purpose of benefiting one party or disadvantaging the other? The second prong, “discriminatory effect,” asks whether the plan exhibits a high level of gerrymandering relative to historical norms. The third prong is “justification,” or whether the state can justify the plan based on its political geography or legitimate redistricting objectives.

The lawsuit alleges that the 2016 congressional redistricting plan fails the test pretty miserably.

Developed by political scientists Nicholas Stephanopoulos and Eric McGhee, the efficiency gap is one way that the courts could measure partisan gerrymandering to determine whether it’s constitutional.

The plaintiffs have asked a federal, three-judge panel to take on the case. The courts should take a close look.

Patrick Gannon is the columnist for the Capitol Press Association.