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Extreme Gerrymandering & the 2018 Midterm

Summary: A new Brennan Center report finds that thanks to extreme gerrymandering, Democrats would need to win by a near eleven-point margin in 2018 to take back a majority in the U.S. House.

Published: March 23, 2018

Many Demo­crats are optim­istic about their chances of winning a major­ity in the U.S. House of Repres­ent­at­ives in the 2018 midterm elec­tions. But in a new report, we meas­ured how much harder partisan gerry­man­der­ing will make it for Demo­crats to win seats — and found that even a blue wave elec­tion akin to 2006 would be far from enough. Maps drawn after the 2010 tea-party wave to favor Repub­lic­ans, partic­u­larly in big swing states like Michigan, North Caro­lina, and Ohio, mean Demo­crats would need to win the national popu­lar vote in 2018 by the biggest margin in a midterm since 1982.


The 2018 elec­tions will test the grip of modern gerry­man­der­ing. Voters appear poised to speak loudly. Early indic­a­tions point to an excep­tional wave elec­tion. But will that voice trans­late into elect­oral results?

While Amer­ic­ans have had wave elec­tions before, one complic­at­ing new factor this decade is the pervas­ive­ness of extreme gerry­man­der­ing in the draw­ing of congres­sional maps. Both parties gerry­mander when they can but the prac­tice has been worsened by increas­ingly soph­ist­ic­ated data and map-draw­ing tech­niques. The U.S. Supreme Court considers two partisan gerry­man­der­ing cases this year, but rulings will come too late to likely affect the 2018 elec­tions. Instead, Amer­ic­ans in key states will vote again under gerry­mandered maps that thus far have proven highly resist­ant to change.

This compre­hens­ive study poses a stark warn­ing to both courts and the public. What looks to be one of the most import­ant recent midterm elec­tions may turn out, in fact, to show how effect­ively extreme gerry­man­der­ing distorts Amer­ican demo­cracy and blunts the public’s voice.

Because of maps designed to favor Repub­lic­ans, Demo­crats would need to win by a nearly unpre­ced­en­ted nation­wide margin in 2018 to gain control of the House of Repres­ent­at­ives. To attain a bare major­ity, Demo­crats would likely have to win the national popu­lar vote by nearly 11 points. Neither Demo­crats nor Repub­lic­ans have won by such an over­whelm­ing margin in decades. Even a strong blue wave would crash against a wall of gerry­mandered maps.

This high barrier to a Demo­cratic major­ity is at odds with early polls show­ing Demo­crats with a signi­fic­ant advant­age in the generic congres­sional ballot. As of mid-March, Demo­crats held an aver­age lead of nearly eight percent­age points, 48–40. Based on histor­ical elec­tion results, a lead of this magnitude should net Demo­crats around 30 addi­tional seats — comfort­ably more than the 24 they need to retake control of the U.S. House of Repres­ent­at­ives. Because of gerry­man­der­ing, however, that is no longer the case. Even the court-ordered redraw­ing of Pennsylvani­a’s congres­sional map will only improve Demo­crats’ chances slightly.

The dispar­it­ies are sober­ing. This decade, gerry­man­der­ing has helped Repub­lic­ans. In the future, it may help Demo­crats. Although this report focuses on Demo­crats, its warn­ings apply with equal force to Repub­lic­ans.

To be sure, Demo­crats might carry some districts they are not projec­ted to win. The March 13, 2018 special elec­tion in PA-18 is a recent example. But surprise results under remark­able polit­ical circum­stances should not obscure the more funda­mental lesson of this decade’s maps — gerry­man­der­ing matters and it matters a lot. Even if 2018 proves to be an unusual year in a greater than normal number of districts, and produces a surprise surplus of Demo­cratic wins, the effects of gerry­man­der­ing will return with a vengeance if 2020 looks more like 2012, 2014, or 2016.

Indi­vidual states paint an even clearer picture. As gerry­manders become ever more soph­ist­ic­ated, generic ballot leads no longer effect­ively predict how many seats a party might pick up. Some state maps are care­fully designed to with­stand signi­fic­ant elect­oral swings while others respond more nimbly to shift­ing polit­ical pref­er­ences. Thus, even if 2018 sees a fairly consist­ent — and even sizable — national shift in favor of Demo­crats that is replic­ated in the states, the party’s seat yield is likely to vary signi­fic­antly between gerry­mandered and non-gerry­mandered states. While seat turnover in non-gerry­mandered states might be close to the number predicted by historic data, gerry­mandered states will see lower rates of change or, perhaps, even no change at all.

Polit­ical scient­ists call the rela­tion­ship between the votes a party gets in a state and how many seats it picks up “respons­ive­ness.” In a highly respons­ive map, a party stead­ily increases its seats as it increases its share of the vote. That is how most assume a demo­cracy should func­tion. A non-respons­ive map would be the reverse: one in which a party can increase its vote share by 10 or even 20 percent without gain­ing a single extra seat. A hand­ful of states have non-respons­ive maps that are espe­cially stark:

  • In Michigan, even if Demo­crats win five seats with 38.38 percent of the statewide vote, they are not projec­ted to compete for a sixth seat until their statewide vote share reaches 54.89 percent, an increase of 16.51 percent­age points. 
  • In North Caro­lina, even if Demo­crats win three seats with 29.66 percent of the statewide vote, they are not projec­ted to compete for a fourth seat until their statewide vote share reaches 52.78 percent, an increase of 23.12 percent­age points.
  • In Ohio, even if Demo­crats win four seats with around 26.07 percent of the statewide vote, they are not projec­ted to compete for a fifth seat until their statewide vote share reaches 54.71 percent, an increase of 28.64 percent­age points.
  • In Texas, even if Demo­crats win 11 seats with around 31.92 percent of the statewide vote, and because of court-made modi­fic­a­tions to the map, compete for a twelfth seat at around 41.07 percent of the vote, they will not compete for a thir­teenth seat until their statewide vote share reaches 51.15 percent, an increase of 10.08 percent­age points.

The dispar­ity is even greater when look­ing at the vote share needed to win a bare major­ity of the congres­sional deleg­a­tions of highly gerry­mandered states.

This study is the first to gauge the magnitude of change neces­sary on a state-by-state basis to flip seats under current congres­sional maps and the first to visu­al­ize the respons­ive­ness of maps, high­light­ing the stark differ­ences between gerry­mandered and non-gerry­mandered states.

It also illus­trates the need for clear legal bound­ar­ies in the age of compu­ter­ized gerry­man­der­ing. Although gerry­man­der­ing has long been a feature of Amer­ican polit­ical life, this decade’s maps durably lock in advant­ages for both parties with unpre­ced­en­ted preci­sion. Even when an elec­tion sees massive changes in the votes a party receives, there can be zero change in the number of seats that party can expect to win. An effect­ively gerry­mandered state’s congres­sional deleg­a­tion can remain completely static unless confron­ted with a true tsunami in favor of one party.

This state of affairs turns on its head the Framers’ notion that frequent elec­tions would ensure Congress was a “mini­ature, an exact portrait” of the people as a whole. While much of the focus in partisan gerry­man­der­ing litig­a­tion has been on meas­ur­ing the degree of bias, even more troub­ling is the lack of respons­ive­ness in this decade’s maps. Regard­less of the 2018 midterms’ outcome, this report’s find­ings serve as a wake-up call: courts must act to rein in extreme partisan gerry­man­der­ing or 2021’s redis­trict­ing will see even more unre­spons­ive, durable, and undemo­cratic congres­sional maps.