Has gerrymandering hurt Democrats this decade?

For House Democrats, the 2021 congressional map may seem disappointing. Congressional Democrats will start the next term with one of the slimmest majorities in decades after losing some close races.

Not since 1893 have the Democrats presided over such a razor-thin majority in the House. Over the past decade, Democrats held a majority in the House only two times.

So, why is it so hard for Democrats to win? Well, one sign points to how our congressional maps are drawn. Some argue that gerrymandering provides structural advantages for Republicans.

Importantly, Republicans convincingly won state houses this cycle too, ensuring that many of these representatives will be able to mark up the congressional maps in their favor again for the next decade.

And, while there are conflicting theories on the exact ways that gerrymandering can impact the competitiveness of races, generally, when one party controls the process, partisan control strengthens. In modern American electoral politics, gerrymandering has become an unforgiving, exacting science. Since the 1990s, mapping software and granular census data gave partisan redistricting a rigorous precision that allows cartographers to optimize districts to the benefit of the party that draws them. 

In the 2010 election, Republicans won many state legislatures and governorships in the lead up to redistricting following the 2010 Census, allowing them to calibrate congressional and state districts in their favor, dividing areas and demographics that may benefit Democrats. When Democrats get the chance, they do it too, but they did not win the opportunity to the same extent as the GOP ten years ago.

Examining models built by the Brennan Center ahead of the 2018 midterms, Democrats need to win more decisive victories on the generic ballot to translate that overall support from the public into congressional wins. According to this research, the countervailing forces of gerrymandering explain why.

But, that’s not to say that Democrats weren’t able to overcome the challenge that year.

The fact that Democrats seized control of the House and won many seats in the 2018 blue wave was a testament to the wide lead they held on the generic ballot. In the lead up to Election Day 2018, the generic ballot put Democrats close to eight points ahead of Republicans. Ultimately, that translated to Democrats winning 41 seats.

The Democrats’ 2018 win was on par with majorities that Republicans held in the House for the better part of the decade. Yet, by contrast, the GOP was able to net these comparable majorities in the House without public sentiment being squarely in their favor on the generic ballot, as the chart below shows.

Republicans' ability to efficiently win seats in the House, and the presidency for that matter, when public sentiment is not in their favor is nothing new.  Now, as the Census comes to a close and redistricting begins in state Houses, many of which are controlled by the GOP, more of the same likely will continue.

In fact, partisan redistricting is likely to get more precise following this next round of decennial redistricting aided by more granular, personal data mined by marketing and online companies. Using these data streams is already at work in optimizing political ads but has yet to makes its way into gerrymandering in the same way. Some experts believe that very well could change this time around.

That would underscore the importance gerrymandering plays in state legislatures and the House. Given GOP control of many state Houses as redistricting gets underway next year and the innovations in mapping technology, Democrats will likely continue to fight an uphill battle for control of the House for the next decade to come.