Eau Claire, Wis. – Wendy Sue Johnson can look out her bedroom window in the 91st Assembly District and see across her side yard into the 68th District. Her house was in the 68th until Wisconsin lawmakers redrew state legislative borders in 2011.

Republicans, who had just won control of the Legislature, rearranged districts that year to maximize the number of seats their party would win.

It worked. In 2012, Republican candidates collected 48.6 percent of all votes cast in Assembly elections, but they won 60 of 99 Assembly seats.

Johnson is among 12 Democratic plaintiffs who challenged the constitutionality of the new map. A federal court agreed with them in November. The U.S. Supreme Court will hear the Wisconsin case in October, setting the stage for historic changes to a bedrock political process and the balance of power in state capitals.

"It's very important not just for Wisconsin, but for districts around the country — including Minnesota," said Justin Levitt, a professor at Los Angeles' Loyola Law School. "One way or another, this will change the rules."

All states draw new legislative and congressional boundaries the year after the decennial census. It's called gerrymandering when the process results in oddly shaped districts meant to give one political party a lopsided advantage.

In a time of deepening divisions across the nation, this arcane yet high-stakes procedure is getting new scrutiny from courts — and from those who want to diminish political hostility and dysfunction.

The case could ease the "sense of distrust between the parties," said Barry Burden, a political scientist and director of the Elections Research Center at the University of Wisconsin, Madison. "I don't think it can get much worse."

Johnson's old district, the 68th, was reconfigured to exclude Eau Claire's traditionally Democratic voters and cluster them in another reworked district, the 91st. The theory behind the move: Sequester Democratic voters in one district so they're less likely to affect election outcomes in neighboring districts.

That amounts to allowing elected officials to choose their voters instead of the other way around, said Johnson, a family lawyer and former social studies teacher. "Just because you can do something doesn't mean you should," she said.

Wisconsin's attorney general, a Republican, has defended the redistricting process as "entirely lawful and constitutional."

The case, Gill vs. Whitford (named for Beverly Gill, chair of the state Elections Commission, and lead plaintiff William Whitford), argued that Wisconsin's redistricting in 2011 was unconstitutional because it violated Democratic voters' guarantee of equal protection under the 14th Amendment and freedom of association under the First Amendment.

The federal trial was the first in three decades to deal with gerrymandering.

On Nov. 1, the U.S. District Court ruled 2-1 that Wisconsin's Assembly map was unconstitutional. Judge Kenneth Ripple wrote in an opinion that it ensured that "the number of Republican [Assembly] seats would not drop below 50 percent."

The defendants appealed to the U.S. Supreme Court. When it said last month that it would take the case, Wisconsin Attorney General Brad Schimel said that he was "thrilled."

In a post-trial brief, the defendants' lawyers criticized the District Court's ruling. Equal population, contiguity and avoiding municipal splits were among criteria used in rewriting the districts, they wrote. "The mere presence of partisan intent does not help to distinguish between lawful partisan plans and unconstitutional partisan gerrymanders."

To buttress their argument during the trial, the plaintiffs cited a complex test called the "efficiency gap," which was devised by University of Chicago law professor Nicholas Stephanopoulos and Eric McGhee of the Public Policy Institute of California.

It measures what they call "wasted" votes — those cast for a losing candidate or for a winning candidate in excess of what they needed to win. A gap of 7 percent is considered acceptable under the formula. The gap in Wisconsin was 13.3 percent in 2012 and 9.6 in 2014.

It's important to understand the efficiency gap because it could give the U.S. Supreme Court a way to define what is — and is not — a constitutional level of political advantage after redistricting. The high court has struck down race-based gerrymandering — most recently in a North Carolina case in May — but it has never ruled against a redistricting map because it was unfairly partisan.

But legal scholars say a 2004 case from Pennsylvania suggested that justices are open to doing so if it arrives at the right definition of unconstitutional gerrymandering.

Four justices wanted to strike down Pennsylvania's map then, and four said the question was best left to politicians. Justice Anthony Kennedy sided with his peers who didn't want to get involved, but he said that he "would not foreclose" the possibility of judicial relief "if some limited and precise rationale were found to correct an established violation of the Constitution in some redistricting cases."

So the question is whether the Wisconsin case provides that rationale, Burden said. "It will come down to whether [Kennedy] latches on to the efficiency gap."

If Wisconsin's dozen plaintiffs prevail at the Supreme Court, Burden said, the repercussions will be broad. The state would have to draw new maps quickly to prepare for 2018 elections, he said, and legislative maps in a third of the states would also become unconstitutional because they don't meet the efficiency gap's standard for fairness.

After the 2020 census, every state would have to factor the ruling into its redistricting process, said Ruth Greenwood, senior legal counsel at the Campaign Legal Center, a nonpartisan group based in Washington that's part of the team representing plaintiffs.

The case is not a slam-dunk, Levitt said. "The justices like to police boundaries. They do not like to undo what everybody does," he said.

The composition of the Supreme Court has changed since the 2004 case with the addition of five new justices, making the ruling in the Wisconsin case difficult to predict.

There are cases in other states. A Maryland lawsuit is challenging Democrats' 2011 congressional redistricting.

In Pennsylvania, a lawsuit filed in state court contends that Republican legislators unfairly drew congressional district borders, allowing the GOP to win 13 of 18 districts. Democrats outnumber Republicans in the state.

One focus of that case is the Seventh Congressional District. Its shape has been called "Goofy kicking Donald Duck" and parts are so narrow that in one place it's the width of a restaurant and, in another, the width of an endoscopy center.

"The only explanation for the plan is raw partisan advantage," said Ben Geffen, a Public Interest Law Center lawyer who's working on the Pennsylvania case. "The Supreme Court has consistently said that at some point, a partisan gerrymander crosses the line into unconstitutionality. The Wisconsin case, I think, lays out great arguments for how courts can draw that line."

Some states, including California and Arizona, use independent commissions to draw new maps. In Minnesota, where the state Supreme Court draws district lines if legislators fail to do so, Rep. Sarah Anderson, R-Plymouth, has sponsored a bill that would bar use of a commission.

"Commissions are unelected bodies that cannot be held accountable for their actions like the Legislature can," she said. Her plan, which hasn't been enacted, would add principles such as equal population, compactness and minority representation to law. It would be "a good standard to have in place so we don't have gerrymandering," she said.

Before redistricting, the Trempealeau County, Wis., town of Strum, population 1,100, was in the sprawling 91st Assembly District — the one that was moved and shrunk to encompass Eau Claire — and is now part of the 92nd.

The redistricting fight is "just politics as usual," farmer Andy Pedersen said between errands in Strum. He voted for Trump. Both parties play the game, he said, so "whether the Republicans are in power or the Democrats are, it doesn't make any difference."

Over coffee at the Foolish Pleasure tavern, retired postal worker and Trump voter Sue Larson agreed. "If the Republicans are in, the Democrats have no say. If the Democrats are in, the Republicans have no say," she said.

"They're absolutely right that both parties do this when they have the chance," Greenwood said, but it's worth reminding people that policies they do care about — from taxes to the environment to education — are determined by the makeup of legislatures.

Johnson thinks that's already happening. The Wisconsin case, she said, "has started a really great conversation across the nation."

Judy Keen • 612-673-4234