Data Wonk

Should Evers Sign Redistricting Bill?

It's governor's plan, but gives Democrats only a 17% chance of winning half of all Assembly seats with 50% of state vote.

By - Feb 14th, 2024 12:25 pm
Gov. Tony Evers

Gov. Tony Evers. Photo by Emily Hamer / Wisconsin Center for Investigative Journalism.

On the Election Law Blog, Justin Levitt, a law professor at LMU Loyola Law School in Los Angeles, points to “an oddity in the most recent round of Wisconsin’s redistricting travails.” Here’s how he describes it:

A few weeks ago, the [Wisconsin] Republican legislature tried to short-circuit the court case by passing a plan they claimed was “99% of the way” to the Governor’s map … No Democrat voted for it, and the Governor vetoed it … The legislative leadership has now floated the possibility of … passing the Governor’s proposal as is (including the purported constitutional violation). And still there seems to be Democratic resistance.

Why would the Republican legislature fighting tooth and nail for advantage suddenly try to pass a Democratic Governor’s plan that they claim is constitutionally infirm? And why would Democrats vote against it?

It’s possible that this is just belated resignation: the legislators think that the state Supreme Court is likely to impose an alternative worse for them than the Governor’s map, and are trying to limit their losses by taking the decision out of the court’s hands.

Which is exactly what the Republican Legislature did yesterday, passing the plan advocated by Governor Tony Evers without any changes. Will Evers sign it, as he previously said he would?

Certainly the plan represents a significant improvement in moving away from the current Wisconsin gerrymander. The next graph shows the scores that three of the plans received from two of the scoring systems. The vertical axis shows the score for proportionality calculated by the web site Dave’s Redistricting (DRA). The horizontal axis shows the scores for partisan bias, one of the three measurings used by the consultants hired by the Wisconsin Supreme Court.

Gerrymandering is defined as a strategy to manipulate district boundaries to favor one party over the other. For the proportionality score calculated by DRA gerrymanders that favor Republican are assigned positives numbers; the higher the value number the stronger the bias against Democrats. For the Partisan Bias, calculated by the consultants, the more negative the value the greater is the bias against Democrats.

The graph shows the scores for three of the six plans that were presented to the Supreme Court. The colored dots show the scores for the Assembly map (in blue) and that for the state Senate (in rust). The smaller the scores the maps earn the smaller the bias favoring Republicans is.

Starting at the upper left-hand corner of the graph, are the maps proposed by the Wisconsin Legislature. These maps are basically the current maps tweaked to eliminate noncontiguities. Their high pro-Republican bias is unsurprising because they are based on the maps implemented following the 2010 census, deliberately designed to guarantee continued Republican control regardless of the election results.

The next maps are from the Johnson group of electors. Their brief claims that these maps were designed without the use of data on voting patterns. These maps are somewhat less biased than the Legislature’s maps, but still heavily biased to favor Republicans.

Finally, there are the maps proposed by Governor Evers. Although far less biased than the first two sets of maps, they still favor Republicans’ control of the state Assembly and Senate.

Scores for three plans.

Scores for three plans.

The next two graphs show the odds that each party will win a number of seats that is at least equal to its share of the statewide vote under the Johnson plan and the Governor’s plan. These come from simulations by Professor Matthew Petering and reported in his amicus brief to the Supreme Court. To calculate these probabilities, Peterson used computer simulation to randomly generate a million Assembly and a million Senate elections based on past elections. Testing the six plans against these elections were used to calculate probability distribution of outcomes.

For example, in an election in which each party received 50% of the statewide vote, what is the probability that Democrats will win at least 50% of the Assembly or Senate districts? Put more generally, what is the probability that each party will win a proportion of seats that is at least as large as its proportion of the statewide vote.

The next graph shows the answer to that question if the Johnson plan is adopted. In the case that Democrats won 50% of the vote, the chance that they also won at least half the Assembly districts is a miniscule 0.4%. In the senate election in which Democrats won half the statewide vote, the simulation predicts that their chances of winning at least half the senate seats is 2.4%. (If the plan originally submitted by the Republican-dominated Wisconsin Legislature were adopted instead, the results for Democrats would be even worse.)

Chance of winning a proportional share of seats Johnson Plan.

Chance of winning a proportional share of seats Johnson Plan.

The next graph shows the odds of Democrats and of Republicans winning at least a proportional share of the Assembly and Senate districts under the Governor’s plan for redistricting. Although much less biased than either of the previous plans, the odds are still heavily stacked against Democrats. In the previous example in which Democrats won half the statewide vote, the simulation predicts that the odds of their winning half the Assembly seats are only 16.7%, and half the senate seats are 34.3% of the senate seats.

Chance of winning a proportional share of seats Governor's Plan.

Chance of winning a proportional share of seats Governor’s Plan.

This helps explain the “oddity” Levitt mentions at the beginning of this column. While Republican leaders obviously would prefer the continued power promised by the Legislature and Johnson plans, the governor’s plan still looks pretty good to them. While not at the astronomical level offered by the Johnson or Legislature plans, the governor’s plan still gives them a partisan edge that will make it easier for them then for Democrats to control the Assembly and Senate.

The Governor’s plan would look all the better if the Supreme Court accepts the offer from its expert consultants to develop an improved plan that is more politically neutral than any of the six plans that were proposed by parties to the lawsuit.

Evers has put himself in a box with his promise to sign a clean version of his map. He will likely hear from Democrats on both sides, for and and against the bill. But one thing is clear: Republicans are hoping he signs it.

Categories: Data Wonk, Politics

4 thoughts on “Data Wonk: Should Evers Sign Redistricting Bill?”

  1. Ron Hockersmith says:

    Second graph might need an update?

  2. Bruce Thompson says:

    Thanks for pointing this out. The second of the two graph is for the Governor’s plan and should appear soon.

  3. Bruce Thompson says:

    It’s corrected now. Thanks for letting us know.

  4. Thomas Sepllman says:

    The bus left the Station when the Republicans presented and approved their Plan

    Who is the Legislature to ignore the Supreme Court The time to THINK is long gone Toooooooooo bad

    a little to late she told her mother The rest of the joke is unknown

    Now if Tony want to trade the approval of his appointees including the ones rejected to the ??? Utility Commission then maybe BUT they will not so.

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