At heart of landmark Supreme Court case: a gerrymandered map that has helped lock in huge legislative majorities for Wisconsin GOP

The news Monday that the U.S. Supreme Court will hear a landmark legal fight over Wisconsin’s redistricting plan puts the spotlight on a gerrymandered political map that has helped lock in legislative majorities for the GOP since it took power in 2011.

The key legal question: Can a set of political districts be so stacked toward one party that it violates the Constitution?

Until the court speaks, that is unsettled law.

But while the law is uncertain, the politics are quite clear.

RELATED:U.S. Supreme Court to hear Wisconsin's redistricting case but blocks redrawing of maps

EDITORIAL:Supreme Court should rein in partisan redistricting

Legislative boundaries like Wisconsin’s present a stark civics question:

How meaningful are elections when control of the legislature in a competitive state is largely predetermined by the way the districts are drawn?

There have now been three big election cycles since the current Wisconsin map took effect, featuring three very different outcomes at the top of the ticket.

• In 2012, President Barack Obama, a Democrat, carried the state by 7 points.
• In 2014, Gov. Scott Walker, a Republican, carried the state by 6 points.
• And in 2016, the two parties finished in a virtual tie for president, with Republican Donald Trump beating Democrat Hillary Clinton by less than a point.

But these partisan shifts had little effect on the battle for the 99-seat state Assembly, where the GOP’s margin of control has averaged more than 20 seats under the lopsided map Republicans drew in 2011.

All the numbers show that the GOP’s advantage is real, it is large and it is much bigger than it was under the previous map.

There are many ways to quantify this partisan “tilt.” The lawsuit that’s now before the Supreme Court uses a formula called the “efficiency gap” to calculate how many votes are “wasted” for a party when its voters are “packed” into a smaller number of seats, diluting that party’s overall clout.

But for this analysis, we’ll use a simple, shorthand method:

Take the top-of-the-ticket election results (for president or governor) as a measure of how many people are backing each party in a given election year. Then see how those voters are distributed across the state’s legislative districts to gauge how many seats favor one party or the other in their makeup.

In the 2012 presidential race, Republican Mitt Romney won just 46% of the statewide vote against Obama. But Romney voters outnumbered Obama voters in 56% of the 99 Assembly districts.

In the 2014 governor’s race, Republican Scott Walker won 52% of the statewide vote against Democrat Mary Burke. But Walker voters outnumbered Burke voters in 64% of the 99 Assembly seats.

And in 2016, Trump won 47% of the statewide vote, finishing a fraction ahead of Clinton. But Trump voters outnumbered Clinton voters in 63% of the 99 Assembly seats.

A 'baked-in' advantage

Based on a Journal Sentinel analysis of the past three elections, at least 60 of the 99 Assembly seats are more Republican in their makeup than the state as a whole.

That’s a profound advantage. It means that in a 50/50 election cycle, when there are roughly equal numbers of Democratic and Republican voters statewide, the GOP can be expected to win at least 60 of 99 districts, a “baked-in” edge of more than 20 seats.

It means that even in a bad Republican year, like 2012, the GOP can still pile up large legislative majorities.

And it means that no matter how the political winds are blowing, Republicans will easily outperform their statewide share of the vote when it comes to winning legislative seats.

The top Democrat in the Assembly, Peter Barca of Kenosha, calls the current map “masterfully nefarious.” The federal court that struck down the map last fall said it was designed to “secure Republican control of the Assembly under any likely future electoral scenario.” And recent elections show that the map not only stacks the deck but erodes competition by reducing the number of competitive swing districts to a bare handful.

What’s the defense against these criticisms?

Republicans say their legislative majorities are earned — that they are the product of superior candidates and campaigns.

“We’re just better at recruiting candidates, better at a message,” Assembly Speaker Robin Vos said in a recent interview.

But even if that were true, there’s little evidence to suggest it accounts for the party’s massive legislative majorities. In fact, Republicans are winning roughly the same number of seats you would expect them to win based purely on the partisan advantage they enjoy in the map.

• In 2012, Romney carried 56 Assembly districts (despite losing statewide) and GOP Assembly candidates won 60 seats.
• In 2014, Walker carried 64 districts and GOP Assembly candidates won 63 seats.
• And in 2016, Trump carried 63 districts and the GOP won 64 Assembly seats.

Republicans aren’t dominating the Legislature because they are winning the votes of ticket splitters (ticket splitting has been in steep decline). They aren’t dominating the Legislature because they’re winning on Democratic turf. They’re dominating the Legislature because they enter each election cycle with a large surplus of GOP-friendly seats, thanks to an extremely favorable redistricting plan.

Political geography plays a role

Another defense of the map goes like this: The GOP’s advantage is largely a product of where Democrats and Republicans live. Because Democratic voters are more concentrated in urban areas (especially Milwaukee and Madison), they are “naturally” packed into fewer districts, leaving the party less competitive in the state’s numerous suburban and rural districts.

“I don’t think people fully appreciate that rural America has become much more conservative. And that’s where a lot of districts are,” said Vos.

There is some truth to this argument. These geographic patterns are real. They became even more pronounced in the last election because of Trump’s strength and Clinton’s weakness with rural voters.

But the federal court found that Wisconsin’s political geography doesn’t account for the sheer magnitude of the map’s Republican tilt, and the numbers back that up. Consider the difference between what happened in 2010 under the old map and in 2014 under the new map.

In 2010, 56 of the 99 Assembly seats were more Republican than the state as a whole, based on their vote for governor. That shows that even under the old lines, the GOP had a built-in advantage. But that edge grew suddenly bigger under the new map. In 2014, 62 Assembly seats were more Republican than the state as whole.

Both elections were similar politically, with 6-point Walker victories at the top of the ticket. But the new map created at least six additional GOP-friendly Assembly seats. And just as importantly, it made the most marginal GOP seats “safer” by improving their Republican makeup.

Consider the difference between the 2004 and 2016 elections. Both were virtual toss-ups for president, with Democrats winning by less than a point in 2004 and Republicans by less than a point in 2016.

Under the old map in 2004, 56 Assembly districts had a Republican tilt, based on their presidential vote. Under the new map in 2016, 63 districts had a GOP tilt.

Winner take all?

A third defense of the GOP map goes like this: Redistricting is properly — and inherently —- a political process. So, to the winner go the spoils.

Not every Republican agrees with this. Freshman U.S. House member Mike Gallagher declared his support this month for using nonpartisan, independent commissions in the redistricting process to “ensure politicians aren’t allowed to gerrymander their districts and choose their own voters.”

That’s a rare stance among Wisconsin Republicans, however. They are aggressively defending their map in court.

Vos fundamentally rejected the idea of an independent redistricting process.

“Everyone has a bias. I would rather have the bias be open and in the public,” said Vos.

But that leaves the question of what recourse the public has if it doesn’t like what it sees. Redistricting isn’t like other policies that voters can simply reject by voting out the party that produced them.

A gerrymandered map is the gift that keeps on giving. By its very nature, it serves to entrench in power that party that produced it.