Please note. Throughout this memo partisan baselines for each district are calculated as the average of the 2020 presidential, 2018 gubernatorial, and 2016 presidential elections. Seats “won” by either party are calculated by applying a uniform swing to this partisan baseline. This does not take into account incumbency effects.

Partisan lean of proposed plans

I define a “competitive” seat as one with a partisan baseline of 5 points or less. In other words, neither party typically receives more than 52.5% of the 2-party vote. By this definition, the current maps contain 3 competitive Senate seats. The WI Legislature’s plan would reduce this to 2. Common Sense Wisconsin would raise it to 5. The People’s Map Commission would create 7.

Partisan lean of seats in proposed maps
Democratic Republican
0-5 D 5-10 D Safe D 0-5 R 5-10 R Safe R
People's Map Commission 6 1 8 1 3 14
WI 2011 1 1 9 2 4 16
Common Sense Wisconsin 0 1 9 5 3 15
WI Legislature 0 1 9 2 4 17

Seats by swing

This graph shows the number of Senate seats won by Democrats depending on the statewide vote swing. By far the best map for Democrats is that proposed by the People’s Map Commission. Under this plan, Democrats could expect to win 15 seats in a statewide tie. To win a majority (17 seats), they would need to win the state by about 6.2 points (i.e. 53.1% of the 2-party vote).

The plan proposed by the Wisconsin Legislature is substantially worse than even the existing plan. If that plan were enacted, Democrats would likely win 10 seats in a statewide tie. They would need to win the state by 10.6 points in order to carry a majority of seats (i.e. 55.3%).

 

Democratic electoral performance across selected district plans
seats in statewide tie minimum swing for majority
Common Sense Wisconsin 10 8.7
People's Map Commission 15 6.2
WI 2011 11 8.6
WI Legislature 10 10.6

 

District changes

The map below shows how districts would change under each scheme. Each pin shows the residence of the current incumbent. Toggle between different baselayers to see how the districts would change.

Addresses were retrieved from the incumbent’s most recent election filing. It is possible, even likely, that some legislators have moved since then.

Consequences for incumbents

Please note. All these calculations are based on the most recent address I could find for each incumbents. Some incumbents may have moved, making these results outdated.

As the map suggests, the People’s Map Commission makes the most dramatic changes to the existing map, whereas the WI Legislature’s proposal mostly makes small tweaks. Ninety-two percent of the population would remain represented by their old incumbent under the Legislature’s map. Under half (49%) would be represented by the same incumbent under the Commission’s proposal.

 

Total population with the same incumbent
population
total voting age
Common Sense Wisconsin 80.1% 80.1%
People's Map Commission 49.0% 49.0%
WI Legislature 92.2% 92.2%

 

The WI Legislature’s plan clearly prioritizes incumbent protection. Based on the most recent addresses available, All 33 curent state senators would find themselves in a district with no other incumbents.

By contrast, the People’s Map Commission would create 20 districts with 1 resident incumbent and 7 districts with 0 incumbents residing therein. Five of the new districts would hold 2 incumbents, and 1 would hold 3 sitting legislators.

 

Incumbent protection statistics by plan
Districts with this # of incumbents incumbents in multiple incumbent districts
0 1 2 3
Common Sense Wisconsin 2 29 2 0 4
WI Legislature 0 33 0 0 0
People's Map Commission 7 20 5 1 13

 

The graphs below show how each incumbent’s district would change under each plan. The graphs do not show “new” districts created without a resident incumbent.

For each incumbent, the arrow extends from the partisan baseline of their current district to the partisan baseline of the proposed new district in which they would reside if the plan in question was adopted.

WI Legislature’s Plan

People’s Map Commission Plan

Common Sense Wisconsin Plan

Appendix