MADISON, Wisconsin – With newly elected Scott Walker in the governor’s office and a firm grip on the legislature, Wisconsin Republicans in 2011 had a unique opportunity to redraw the state’s electoral maps and fortify their party’s future.

Aides were dispatched to a private law firm to keep their work out of public view. They employed the most precise technology available to dissect new U.S. Census data and convert it into reliably Republican districts even if the party’s fortunes soured. Democrats were kept in the dark, and even GOP incumbents had to sign confidentiality agreements before their revamped districts were revealed to them. Only a handful of people saw the entire map until it was unveiled and quickly approved.

In the following year’s elections, when Republicans got just 48.6 percent of the statewide vote, they still captured a 60-39 seat advantage in the General Assembly.

Now, the Supreme Court is being asked to uphold a lower court’s finding that the Wisconsin redistricting effort was more than just extraordinary – it was unconstitutional.

Such a conclusion would mark a watershed moment for the way American elections are conducted.

The Supreme Court has regularly – and increasingly – tossed out state electoral maps because they have been gerrymandered to reduce the influence of racial minorities by depressing the impact of their votes.

But the justices have never found a plan unconstitutional because of partisan gerrymandering – when a majority party draws the state’s electoral districts to give such an advantage to its candidates that it dilutes the votes of those supporting the other party.

A divided panel of three judges in Wisconsin, though, decided just that in November. It became the first federal court in three decades to find that a redistricting plan violated the Constitution’s First Amendment and equal rights protections because of partisan gerrymandering.

The Supreme Court could announce as soon as Monday that it is either affirming or reversing the lower court’s decision, or, more likely, accepting the case for full briefing and arguments in the term that begins in the fall.

The case comes at a time when the dusty subject of reapportionment has taken on new significance, with many blaming the drawing of safely partisan seats for a polarized and gridlocked Congress. Barack Obama has said one of his post-presidency projects will be to combat partisan gerrymanders after the 2020 Census.

In Wisconsin, it already has become a hot topic.

“If there’s one word that defines the last year or year and a half in this country, it’s ‘rigged,’ ” said Dale Schulz, a Republican and former Wisconsin legislator who has joined with a Democratic counterpart to urge an end to the way the state handles redistricting. “People have come to realize their votes aren’t as important as they once were. And that’s really what this whole case is about: It’s about making sure people’s votes have equal value.”

Schulz volunteered that he voted for the plan. After some run-ins with leaders of his party, he said he was just glad “they had not put my district in Iowa.” But he said he saw after the maps were enacted that legislators became more beholden to party leaders because the only real threat to reelection was a primary challenge.

Schulz’s Democratic partner in the Fair Elections Project, former state senator Tim Cullen, added that he constantly hears from audiences that if his party had been in charge of the process, it would have done the same thing Republicans did.

“And, of course, the answer to that is Democrats probably would have done the same thing. But that doesn’t make it right,” he said.

In fact, a challenge to the way Maryland Democrats drew districts to squeeze out one of the state’s two Republican congressmen is making its way through the courts, and a complaint about partisan gerrymandering by Republicans in North Carolina already is before the justices.

Wisconsin’s Republican legislative leaders did not grant interview requests, but in their briefs to the Supreme Court, they said that if their redistricting is unconstitutional, so is that of about a third of the other states.

They asked the justices to reject any effort that “wrests control of districting away from the state legislators to whom the state constitution assigns that task, and hands it to federal judges and opportunistic plaintiffs seeking to accomplish in court what they failed to achieve at the ballot box.”

Misha Tseytlin, Wisconsin’s solicitor general who is defending the redistricting plan, said the Republican advantage in the state legislature comes in part because its voters are spread across the state, and because it is winning the battle for voters in the purple state.

“I think that political gerrymandering has become a – I don’t want to say an excuse, but something that a lot of folks who are frustrated by the state-level elections over the last eight years have come to rely on as an excuse,” he said in an interview in the state capitol. “It’s easier to have a villain than to say, oh, our party isn’t doing well, not selling its message or unfortunately for our party our voters are clustering in major cities.”

The Supreme Court has been reluctant to tackle partisan gerrymandering and sort through arguments about whether an electoral system is rigged or, instead, a party’s political advantage is due to changing attitudes and demographics.

The justices last took up the topic in 2004 in a case called Vieth v. Jubelirer. It split the court five different ways, with the bottom line being that the justices could not agree on a test to determine when normal political instincts such as protecting your own turned into an unconstitutional dilution of someone else’s vote.

Four justices – only Justice Clarence Thomas remains of the group – said it was not the court’s business to make such decisions. Justice Anthony M. Kennedy joined the group to decide the specific case against the challengers of a Pennsylvania redistricting plan, but he left the door open for future cases.

Kennedy said he could envision a successful challenge “where a state enacts a law that has the purpose and effect of subjecting a group of voters or their party to disfavored treatment.” What was elusive, Kennedy said, was “a manageable standard by which to measure the effect of the apportionment and so to conclude that the state did impose a burden or restriction on the rights of a party’s voters.”

William Whitford, one of a dozen plaintiffs suing over the Wisconsin plan, said his case, Gill v. Whitford, should be attractive to the Supreme Court: “We think we have a standard.”

Whitford, 77, was born in Madison, Wis. He is a Democratic partisan who lives in an old left-leaning neighborhood near downtown where, he said, “it would take a genius to put me into a Republican district.” But he and the others in the lawsuit say the statewide partisan gerrymander makes it impossible for him to get the government he wants.

“I want to get elected a Democratic majority,” he said. “It is the only chance for me to influence policy.”

Whitford and his fellow plaintiffs asked the Wisconsin court to use a new approach to gauge how Republican mapmaker hurt Democrats with the main tools of gerrymandering: “packing” and “cracking.” These refer to packing like-minded voters, such as supporters of the same party, into a limited number of districts or cracking their influence by scattering them across districts in numbers too small to make an impact.

University of Chicago law professor Nicholas O. Stephanopoulos and his political scientist colleague Eric McGhee, of the Public Policy Institute of California, called their theory the “efficiency gap.” Under their approach, every voter packed into a district above the threshold needed to elect a candidate from his party creates a “surplus” vote. And someone in a cracked district, who votes for a candidate that is unable to win, is a “lost” vote. Surplus and lost votes are considered wasted votes.

The efficiency gap measures the difference between the wasted votes of the two parties in an election divided by the total number of votes cast. In an ideal scenario, where individual votes have as much impact as possible, the efficiency gap would be zero. The gap in Wisconsin was 13.3 percent in 2012.

National groups opposed to partisan gerrymandering hail the theory as just the kind of objective test Kennedy said he was looking for.

The Wisconsin court was not so definitive. It acknowledged the efficiency gap, but only as one of several theories the court said corroborated its findings that the Republican leadership had a discriminatory intent, that its plan had a discriminatory effect and that the state had no legitimate reason for drawing the districts in the way it did.

Tseytlin, the solicitor general, said he finds it “frustrating” that the efficiency gap has been hailed as a way to scientifically measure gerrymandering and said challengers have backed off their reliance on the theory in their Supreme Court filings.

“The actual standard that the district court used was kind of like a social-science mishmash,” he said.

Paul M. Smith, vice president for litigation and strategy at the Campaign Legal Center, which is representing the plaintiffs at the Supreme Court, said his side has not retreated from the idea that the efficiency gap theory could be the test that convinces the Supreme Court but that it was never meant to be the only gauge.

“We don’t think any one formula has to have some kind of talismanic significance,” Smith said, adding that “the conclusion that this is one of the most extreme gerrymanders ever done is supported by the evidence – indeed, it’s compelled by the evidence – and supported by all of the different measures.”

Tseytlin counters that there is plenty of evidence that points to a natural Republican advantage in Wisconsin, where Democratic voters are mostly clustered in Madison and Milwaukee.

Because of its history of split government, Wisconsin legislators and governor have been unable to agree on redistricting plans in the past – the 2011 plan was the first in decades. So the maps have been drawn by federal judges, the “most nonpolitical way someone could draw a plan,” Tseytlin said.

Under those court-drawn plans, Republicans have won a majority of Assembly seats in every two-year election cycle since 1994, with the exception of 2008, the year of the Democratic landslide election of Obama. In 1998, Republicans won 49 percent of the statewide vote but 55 of the 99 Assembly seats, he said. In 2004, the party got 50 percent of the vote and won 60 seats.

“The consequences of political gerrymandering in the real world have been greatly exaggerated,” he said.

Whitford acknowledged Republicans may have something of a built-in advantage, but the 2011 redistricting plan gives Democrats no chance at all, he said.

“I tell people, no harm is going to come from this case,” he said. “But we’ll be lucky to get a level playing field. It may be still tilted, just not as tilted.”