* The Better Government Association has really upped its game lately, smashing or at least challenging some commonly held notions rather than reinforcing them with click-bait pieces. Its latest is a must-read…

In one of those perverse twists of politics, Illinois Republicans hoping to whittle away at Democratic control of Springfield are looking for salvation in an upcoming U.S. Supreme Court case that could undermine GOP might in Wisconsin.

At issue is what could shape up to be a landmark decision on political gerrymandering, a widespread practice dating to the early 19th century in which powerbrokers draw the boundaries of election districts to manipulate the outcome of legislative races.

But a BGA analysis of the statistical underpinnings of the Wisconsin case suggests the Republican minority in Illinois may want to hold off on breaking out the champagne, even if the high court rules against their brethren to the north.

In short, the Justices are being asked to sign off on a lower court ruling that the GOP-controlled Republican legislature in Wisconsin diluted Democratic voting power with surgical precision in drawing a map of new legislative districts after the 2010 Census.

The same calculus used to make that argument for Wisconsin suggests gerrymandering in Illinois is tepid by comparison.

That conclusion flies in the face of the deeply held conviction among many Republicans that mapmaking foul play is the prime reason why powerful Illinois House Speaker Michael Madigan and fellow Democrats have for years remained firmly in control of both the Illinois House and Senate.

To be sure, the analysis of Illinois voting data in no way suggests that majority Democrats who drew the latest legislative maps here did so without putting a thumb on the scale. But the data points to the prime motivation being the protection of incumbents, be they Democrats or Republicans, and a variant of manipulation that the Supreme Court is not being asked to weigh in on.

In recent election cycles, more than 90 percent of races for the Illinois House were either uncontested or involved only token challenges to an incumbent. That phenomenon benefits Democrats in the Chicago area, where the bulk of the state’s population resides, and Republicans Downstate.

“Illinois is really screwed up, but it’s not as screwed up as Wisconsin,” said Cynthia Canary, the former executive director of Change Illinois, which pushed to get a redistricting reform proposal on the November 2016 ballot, only to see it blocked by the Illinois Supreme Court. “There’s a multitude of factors that come into play.”

One of those factors also lies at the heart of the Wisconsin case before the Supreme Court. It is a mathematical formula known as the “efficiency gap,” a measurement of vote distribution developed by Nicholas Stephanopoulos, an assistant professor at the University of Chicago Law School, and Eric McGhee, a research fellow at the nonpartisan Public Policy Institute of California.

Designed to determine whether gerrymandering has enabled one political party to unduly extend its power, the formula compares the difference in so-called wasted votes—either those cast for a losing candidate or those cast for the victor in excess of what was needed to win. The election favors the party with fewer wasted votes, Stephanopoulos and McGhee wrote.

Because each legislative district represents roughly the same number of voters, the calculation can be simplified: The efficiency gap is the difference between the share of seats a party actually wins and the share it should be projected to win based on the average district vote in such contests.

Or mathematically expressed: Efficiency Gap = Actual Seat Share - Projected Seat Share, where Projected Seat Share = 0.5 + 2 × (Vote Share - 0.5)

For example, if the vote math projects that Republicans should win 50 seats in a 100 seat chamber and in reality they snag 57, the efficiency gap is then 7 percent.

Simon Jackman, a professor of political science at Stanford University, analyzed the Wisconsin legislative districts. In his 2015 report, a copy of which was submitted into evidence in the court case, Jackman said the state’s plan drawn by majority Republicans “presents overwhelming evidence of being a pro-Republican gerrymander.”

The efficiency gap for the 2012 and 2014 elections in Wisconsin, the first carried out under the new Republican drawn map, was far greater than the efficiency gap measured in Illinois over the same period.

Prior to the remap, the 99-seat Wisconsin Assembly had 52 Republicans and 47 Democrats. After the remap in 2012, the Republican edge grew to 60 to 38, with one independent.

A host of variables can affect the outcome of individual political races—money, media strategy, name recognition, issues and personalities. In virtually every election there will be some divergence between the share of legislative seats a party wins and the share its collective vote totals indicate it should win.

So Stephanopoulous and McGhee propose an efficiency gap threshold of 8 percent for state house plans. Any map beyond that threshold deserves close scrutiny—including the 2012 maps for Wisconsin, Ohio and Indiana, but not Illinois, according to BGA analysis.

While the Supreme Court’s decision to hear the Wisconsin case has raised hopes that it might provide some legal guidance or clarity in legislative map-making, history suggests there are good reasons to keep expectations in check. The court has shown itself to be more comfortable dealing with racial and voting rights challenges to redistricting, but reluctant to venture into the tricky waters of gerrymandering for purely political ends.

However the ruling comes out, it is likely to attract attention far beyond the political map in Wisconsin. A recent analysis by the Associated Press of the effects of redistricting in hundreds of congressional and state legislative races showed Republicans had a clear advantage in traditional battleground states such as Florida, Michigan, North Carolina, Pennsylvania, Virginia and Wisconsin, where political districts were drawn by Republicans after the 2010 census.

If the decision is upheld, that could directly affect the drawing of individual state political boundaries after the 2020 Census is completed—or not. It’s difficult to speculate on the possible impact of the Supreme Court’s decision, Canary said, stressing that it could be crafted to apply broadly or written narrowly to just impact Wisconsin. And there’s always the possibility as well that the court could overturn the lower court ruling, effectively siding with the status quo and giving the green light to politically motivated gerrymanders.

Whatever the court rules will be thrust, for Illinois, into the political reality of Democratic Party dominance, especially in the metropolitan Chicago area. The party’s advantage may have less to do with lines on a map than with voter behavior that increasingly defines the state as a Democratic Party behemoth in the mold of New York and California.

“You’re not going to change the demographic and political culture of Illinois just by changing the lines,” said David Yepsen, the former director of the Paul Simon Public Policy Institute at Southern Illinois University Carbondale.

While all the Midwestern states surrounding Illinois went for Republican Donald Trump in the 2016 presidential election—some by double-digit margins—Hillary Clinton carried the Prairie State by almost 17 percentage points.

Clinton prevailed in all but one of the six counties that make up metro Chicago, grabbing 58 percent of the combined vote. Meanwhile, Democratic U.S. Senate candidate Tammy Duckworth trounced Republican incumbent Mark Kirk by 15 percentage points.

The political might of Chicago and the surrounding counties holds huge sway over the remainder of Illinois. Sixty-three percent of the votes cast in the 2016 election came from metro Chicago. No other Midwestern state in the area has a metropolitan area with comparable political influence, and the Chicago region—not just the city itself—is tacking ever more Democratic.

That reflects a national urban-rural divide, where Democratic candidates draw from major population centers while Republicans like Trump, draw from rural and small town America.

The disadvantage to Illinois Republicans is that the vast majority of Downstate counties are losing population while Chicago and its environs become a “super urban metro area,” said Charles Franklin, a professor of law and public policy at Marquette University Law School in Milwaukee.

“It’s hard to design districts that break into that urban bloc, that shatter that large population,” Franklin said.

The degree of the partisan benefit from district maps is in dispute. Jackman found that President Obama won 53.5 percent of the two-party Wisconsin presidential vote in 2012, yet Democrats won only 39.4 percent of that state’s 99-seat legislature.

By contrast in Illinois, the share of state house seats won by Democrats roughly mirrored the share of the presidential vote that Obama got that year. Obama captured nearly 58 percent of the Illinois vote in 2012 and Democrats won 60 percent of house seats.

By the 2014 elections, according to a study done by Canary and University of Illinois Springfield political scientist Kent Redfield, “partisan bias” in the legislative maps was more clearly benefiting Democrats.

All 118 seats in the house were up for election that year and the combined votes cast in those races was almost evenly split between Republican and Democratic candidates, Redfield and Canary noted in a report released in 2015. Even so, Democrats won 71 house seats to 47 for Republicans.

Political partisans—usually those out of power—have complained about gerrymandering since the early 19th century, after a salamander-shaped district was part of a mapping plan approved by then Massachusetts Governor Elbridge Gerry. Complaints have been remarkably consistent.

“It is an elaborate and rigged system that is failing the people of Illinois. It only works for the political insiders,” complained Republican Gov. Bruce Rauner, whose agenda has run into a brick wall of resistance from legislative Democrats.

What redistricting has clearly done in Illinois is preserve the careers of incumbents of both parties. That report by Canary and Redfield found that from 1992 through 2014 the percentage of uncontested or non-competitive primaries in both parties ranged between 85 percent to 95 percent in state House races.

“The problem is we’re not looking at maps drawn to represent neighborhoods or communities but to protect incumbents and still be in compliance with the Voting Rights Act,” Canary said. “Protecting incumbency has been the dominant imperative.”

For Illinois Republicans, a decision in the Wisconsin case holds the potential of being unsatisfactory, regardless of the outcome.

If the high court affirms the federal panel’s decision, it could have a significant impact on Wisconsin, and perhaps several other states with maps skewed to favor Republicans, while leaving Illinois unaffected. That would be because Illinois maps appear less partisan according to the standard under court review.

And if the court decides to leave the Wisconsin map in place, the status quo would also be preserved in Illinois.

“There are a lot of expectations, but this is not likely to be a solution necessarily writ large across the board,” Canary said. Depending on the outcome of the case, she said, it could encourage lawsuits in other states alleging improper political gerrymandering.

“But it won’t turn Democrats into Republicans and Republicans into Democrats,” Canary said.