The Wisconsin legislative map at the heart of the U.S. Supreme Court’s closely watched redistricting case is a stark example of how district lines can be drawn to keep one party in power in a very purple state no matter how it is faring at the ballot box. In good times and bad, Wisconsin Republicans have enjoyed a virtual lock on the 99-seat state Assembly, thanks to the map they drew in 2011. Their control of the Legislature is essentially baked in before voters go to the polls to pick their representatives. How tilted is the map? Here is one way to measure it: Take the top-of-the-ticket statewide election results (for governor or president) as a measure of how many people are supporting each party in a given year. Then see how those voters are distributed across the state’s 99 Assembly districts to find out how many seats favor each party.
In 2012, Republican Mitt Romney won just 46% of Wisconsin’s two-party presidential vote against Democrat Barack Obama. Under a “neutral” Assembly map that offered no built-in advantage to either party, Romney voters would have outnumbered Obama voters in 46 of the 99 Assembly seats, reflecting their statewide share of the vote. Instead, Romney voters outnumbered Obama voters in 56 seats.
In 2014, Republican Walker won 53% of Wisconsin’s two-party vote for governor against Democrat Mary Burke. Under a neutral map, Walker voters would have outnumbered Burke voters in 53 Assembly seats. Instead, Walker voters outnumbered Burke voters in 64 seats.
In 2016, Republican Donald Trump won just over 50% of Wisconsin’s two-party vote for president against Democrat Clinton. Under a neutral map, Trump voters would have outnumbered Clinton voters in 50 of the 99 Assembly seats (a one-seat advantage). Instead, Trump voters outnumbered Clinton voters in 63 seats (a 27-seat advantage).