Skip Navigation

New Report: Extreme Partisan Maps Account for 16–17 Republican Seats in Congress

A new report finds that extreme partisan bias in congressional maps account for at least 16–17 Republican seats in the current Congress and that only a small number of swing states account for the vast majority of this partisan skew.

May 16, 2017

The 2018 midterms will be fiercely fought, with a focus on control of the U.S. House after years of Repub­lican domin­ance. At the same time, the U.S. Supreme Court will likely hear a chal­lenge to partisan gerry­man­der­ing in Gill v. Whit­ford later this year. And both parties gear­ing up for the new national redis­trict­ing cycle start­ing in 2021. Congres­sional maps are back in the polit­ical spot­light.

Today, a new report from the Bren­nan Center for Justice at NYU School of Law finds that extreme partisan bias in congres­sional maps account for at least 16–17 Repub­lican seats in the current Congress –a signi­fic­ant portion of the 24 seats Demo­crats would need to gain control of the House in 2020 – and that only a small number of swing states account for the vast major­ity of this partisan skew.

Extreme Maps, the first in-depth report to use data from the 2016 elec­tion as well as the 2014 and 2012 cycles, focuses on the most egre­gious map-draw­ing abuses. The congres­sional maps in ques­tion have high levels of “partisan bias” – the degree of system­atic advant­age one party receives over another in turn­ing votes into seats – under at least three widely accep­ted stat­ist­ical meas­ures. Among the find­ings:

  • This decade’s congres­sional maps consist­ently bene­fit Repub­lic­ans: In the 26 states that account for 85 percent of congres­sional districts, Repub­lic­ans derive a net bene­fit of at least 16–17 congres­sional seats in the current Congress from partisan bias – signi­fic­antly more than previ­ously thought.
  •  Extreme maps have proved remark­ably durable: Typic­ally, the impact of biased maps drawn by state legis­lat­ors lessens over the years as voters move, popu­la­tions change, and legis­lat­ors retire. But this time, the maps’ high levels of partisan bias have persisted through both pro-Repub­lican and pro-Demo­cratic elec­tions.
  •  Just six swing states and Texas account for almost all the bias: Michigan, North Caro­lina, and Pennsylvania consist­ently have the most extreme meas­ures of bias, account­ing for at least 7–10 Repub­lican seats in each elec­tion since the 2011 redis­trict­ing. Flor­ida, Ohio, Texas, and Virginia jointly account for most of the remain­ing extra Repub­lican seats. All these states had one-party control of the process.
  •  Maps drawn by inde­pend­ent commis­sions, courts, or split-party state govern­ments had less bias: There is strong evid­ence that less partisan redis­trict­ing processes have led to less biased maps; no maps drawn since 2011 by these means had high level of bias across all three elec­tion cycles since. Conversely, maps in each of the seven states with the worst gerry­man­der­ing abuses were drawn under single-party control.

“Gerry­man­der­ing can mean many things to many people,” said Michael Li, senior coun­sel in the Bren­nan Center’s Demo­cracy Program and co-author of Extreme Maps. “Among the most danger­ous forms of gerry­man­der­ing is when redis­trict­ing locks in an unfair share of seats for one party. Courts have struggled in the past to stop this sort of abuse because it’s been hard to meas­ure. But the last three elec­tions show clear, meas­ur­able evid­ence that perni­cious map-draw­ing abuses are a feature in a few key states – giving the courts the impetus and inform­a­tion they need to act. ”

“Gerry­man­der­ing has been a prob­lem since our nation’s found­ing,” said Wendy Weiser, director of the Bren­nan Center’s Demo­cracy Program. “But today, maps in a few states are so egre­giously biased in favor of one party that they can be right­fully called ‘extreme.’ These extreme maps in only a hand­ful of swing states completely warp the compos­i­tion of Congress.  They are the product of a flawed, undemo­cratic process, which usurps the basic power of voters to choose their repres­ent­at­ives.”

Read the full report, Extreme Maps.

Read more about the Bren­nan Center’s work on Redis­trict­ing.

For more inform­a­tion or to sched­ule an inter­view, contact Blaire Perel at (646)925–8734 or perel­b@bren­