From a Brennan Center for Justice at NYU School of Law press release:

With a solid lead in national polls and a string of special election victories, Democrats are optimistic about their chances of winning control of the House this fall. But a new report from the Brennan Center for Justice at NYU Law shows that the impact of extreme gerrymandering could severely hamper those efforts. Democrats would need a near-record 11-point national margin or a series of extraordinary breaks to win the narrowest of majorities in the chamber.

Extreme Gerrymandering and the 2018 Midterms is the first comprehensive study of the overall electoral impact of this decade’s politically skewed congressional maps. The Supreme Court is set to rule on the legality of extreme partisan gerrymandering this term — Wednesday, justices will hear a case on a map that favors Democrats in Maryland — but any rulings will likely come too late to impact the 2018 elections. State-by-state, the new Brennan Center report shows how extreme maps this cycle could hobble Democrats’ ambitions and impact our democracy.

“Because of partisan gerrymandering, one of the most pivotal midterm elections in recent memory could see many Americans’ votes simply be for naught,” said Michael Li, senior counsel in the Brennan Center’s Democracy Program and a co-author of the report. “New technology is making gerrymandering ever more sophisticated — districts can be locked in for one party through good and bad election cycles alike, without voters ever having a meaningful choice. If the Supreme Court doesn’t act, we’ll likely see even more unfair maps next decade.”

This fall, elections in several swing states key to Democrats’ electoral ambitions could be especially impacted by heavily gerrymandered maps:

• In Michigan, Democrats can win five of 14 seats with around 38.38 percent of the statewide vote, but the Brennan Center projects the party is unlikely to compete for a sixth seat until their statewide vote share reaches 54.89 percent, an increase of 16.51 percentage points and a level that Democrats have reached only once in the last six elections.
• In North Carolina, Democrats pick up three of 10 seats with 29.66 percent of the statewide vote, but the Brennan Center projects they will be unable to compete for a fourth seat until their statewide vote share reaches 52.75 percent, an increase 23.1 percentage points and a level they reached in the last six elections only in the 2008 Obama wave election.
• In Ohio, Democrats win four of 16 seats with around 26.07 percent of the statewide vote, but the Brennan Center analysis shows they do not compete for a fifth seat until their statewide vote share reaches 54.71 percent, an increase of 28.64 percentage points and a level they have not managed to reach in any of the last six elections.

Extreme Gerrymandering and the 2018 Midterms measures what’s known as responsiveness in congressional maps – the link between gaining votes and picking up congressional seats. States with maps drawn by independent commissions or courts, like California, are highly responsive to voters. The worst gerrymanders appear in states where maps were drawn under single-party control to lock in a party’s stranglehold on power.

“Our report reveals the incredible gap between shifts in voter preferences and likely election outcomes,” said Laura Royden, researcher in the Brennan Center’s Democracy Program and report co-author. “Whether you’re a Democrat or a Republican, you should be outraged that our democracy is distorted by maps that are intentionally designed to undermine a fair vote.”

Read the full report, Extreme Gerrymandering and the 2018 Midterms.

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