Redistricting and Partisan Balance: The New House Map Might Favor Democrats

For long-time watchers of cable news, it’s long been taken as a given that the House of Representatives has a semi-permanent Republican skew due to gerrymandering and geographical bias. Since the emergence of project REDMAP in 2010, in which Republicans crafted gerrymandered maps that drew several red-state Democrats out with surgical levels of precision, the GOP has enjoyed a consistent and clear edge in the House, to the point where the chamber was considered Safe Republican in anything but the bluest of waves.

For an example of this, look to 2012, where Democrats won the congressional vote by a point and ended up with a 17-seat minority. Reflecting how deeply entrenched this bias was, some outlets predicted that the party would need to win the popular vote in 2018 by over ten points in order to break through the House’s Republican lean. However, most of these analyses missed how educational polarization-fueled realignments complicated the calculations significantly, and thus ended up being very wrong; in fact, in 2018, the tipping point seat was a relatively modest 4 points right of the nation. This continued in 2020, where the House’s Republican bias dwindled to approximately 2 points in margin.

Due to a cycle in which Democrats failed to flip nearly as many state legislative chambers as they had hoped, however, many once again feared a repeat of 2010 in redistricting. Entering 2022, the assumption was that the GOP would easily net enough gains through re-gerrymandering red-state congressional maps to flip a House decided by only 5 seats.

The only problem is that this is not how things have played out so far. In fact, it looks increasingly likely that the Congressional map for the 2020s may be biased towards Democrats, even in a neutral environment.

Redistricting 2021: A Consensus

The Republican House bias of the last decade can trace its roots back to the 2010 wave, a pivotal election cycle that delivered countless state governments into GOP hands. After netting 680 legislative seats and 6 governorships, Republican trifectas were in charge of drawing 218 House seats in 22 states – a majority in the chamber by itself. The establishment of REDMAP by party operatives further aided Republicans in drawing congressional and legislative maps designed to fortify their midterm gains. While Florida, North Carolina, and Pennsylvania’s original lines would go on to be struck down mid-decade, potent gerrymanders in Ohio, Michigan, and Texas remained. Democrats had some redistricting victories in states like Illinois, but these were not enough to offset the Republican advantage in the House.

Given the carnage of the 2010 redistricting cycle, many Democrats were still skeptical of their chances of success before the beginning of the belated 2020 redrawing process. Much hesitance also stemmed from the fact that Republicans controlled redistricting in 19 states, outnumbering Democrats, independent commissions, and split control. Furthermore, given that Republicans had inherent advantages in important states like Texas, Florida, Georgia, Ohio, and North Carolina, Democratic apprehension was not misplaced.

Let’s start with obvious points of Republican success from this redistricting cycle. In New Hampshire, Georgia, Texas, Indiana, Utah, Oklahoma, and Tennessee, the GOP used its complete control to pass effective gerrymanders. Depending on November, those maps will probably net up to 7 seats for Republicans while locking in previous gains. Another GOP break came in Maryland, where the legislature passed a likely 7-1 map with a competitive 1st district that Republicans are favored to hold this year. By drawing maps that could have been much more favorable for Democrats, independent commissions in Arizona and Colorado also spared Republicans. Unless Florida pursues an aggressive 19-9 or 20-8 gerrymander, that’s where GOP success ends.

Meanwhile, Democrats benefited from carefully crafted gerrymanders in New York and Illinois. In Nevada, New Mexico, and Oregon, Democratic maps are likely to hold up for the remainder of the decade, even if Republicans win competitive Biden-won seats in each this fall. 

Commission maps in California, Virginia, New Jersey, and Michigan all benefit Democrats to certain extents. Republicans also appear disinclined to draw out Democratic seats in Kansas City and Louisville. But it has been the late-breaking court victories in otherwise-hostile states that have augured best for Democrats.

The shift began with Ohio, where the court struck down a gerrymander that seemed likely to produce a 13-2 Republican delegation in the midterms. Now Democrats will probably get 5 Biden-won seats to play with, a much better floor even if the environment costs them 1 or 2 of those seats this fall. North Carolina’s court produced a similar outcome by striking down a map that could have elected an 11-3 Republican delegation. Redistricting in the Tar Heel State could now result in a 7-7 split.

In Pennsylvania, the court intervened to prevent a Trump-oriented judge from determining the lines, opening the path for a fair map that will probably resemble one adopted in 2018. Alabama’s map was also struck down, and a favorable VRA litigation outcome for Democrats could produce up to 3 more Black-majority seats in the South (AL, LA, SC).

In the end, a combination of late-breaking court victories turned the tide of the redistricting cycle toward Democrats. Favorable maps will almost certainly not be enough to curb Republican momentum in 2022, but they will make it difficult for the GOP to hold the House under hostile national conditions in the future.

Quantifying House Bias

So how do we quantify the partisan balance of the new House map? The key question marks in redistricting revolve around Florida, Ohio, and North Carolina – for the purposes of this exercise, we’ll assume Florida goes with a map that yields 18 Trump-won seats and 10 Biden-won seats, with one of those Biden-won seats denoted as close, giving him 51.3% or less of the vote share (for shorthand, we’ll denote this split as 18R-9D-1C). For North Carolina, we’ll use a map that has an 8R-6D split, and for Ohio, we’ll use a map that has a 10R-4D-1C split. Lastly, for Pennsylvania, we’ll use an 8R-7D-2C split, which we view as the most conservative plausible outcome at this point. We also won’t assume extra Black-majority seats in South Carolina or Louisiana, but we will assume that Alabama gets one, because the court-ordered redraw has now begun as of the morning of Monday, February 7 without the Supreme Court stepping in.

To approximate the bias of the House map for the upcoming decade, we can assess the partisan lean of districts by their 2020 presidential vote. Before we do this, however, we’ll first need to introduce the concept of the tipping-point seat. In 2020, Joe Biden beat Donald Trump in the popular vote by roughly 4.5%. If we ranked every congressional district by Biden’s win margin, we’d find that Biden beat his national margin in 213 out of 435 seats. A party needs to win 218 seats to win the House, and Biden won the 218th seat, defined as the tipping-point, by only 2.8%. This means that in 2020, the 218th seat voted to the right of the nation by 1.7%, meaning that in a neutral environment where the national vote was 50/50, Republicans would have won the tipping-point seat by 1.7% under the old set of maps.

Now, however, things are different, thanks to the circumstances outlined in the prior section. As things currently stand in redistricting, the tipping-point seat is likely to be approximately Biden +6, which would give the House a ~1.5 point Democratic bias by presidential vote. Moreover, with our current projections, 219 seats would have been counted as left of the nation by this metric.

A similar story emerges when using vote share instead of margin; when using vote share, the 218th seat is likely to have given Biden about 0.5% more in raw vote than his national share of 51.3%. 218 seats would be left of the nation, which is exactly the amount required for a majority. Both of these metrics point to the same underlying story: that the House could have a Democratic bias for the first time in over a decade.

It is important to remember that these are not perfect estimates and that there are error bars; for example, if Florida, Pennsylvania, and North Carolina go with plans that are slightly more generous toward Democrats, this number could go up to 222, and if two more Black-majority seats emerge in South Carolina, and Louisiana, it could rise as high as 224. This would give the House a Democratic bias of a shade over 2 points by two-way presidential margin. On the flip side, if Alabama, Florida and North Carolina adopt the harshest plausible plans, we could see this number go down to 216, which would give the House a small Republican lean of about a point. We believe the window of plausibility for House bias here is thus likely to be between R+1.5 to D+2.5, with a median of D+1.

One more open question is what the “floor” for parties will be. One way to examine this is to see the number of districts in which a party received at least 54% of the vote; in the D+8 environment of 2018, Democrats flipped only four districts in which Trump received 54% or more. In 2022, we estimate there will be ~200 seats in which Biden received this share of the vote; thus, barring a 2010-esque wave materializing, it seems unlikely Democrats will fall below 200 seats. For Republicans, this number is at around 170; however, given that House Republicans typically run a point or two ahead of the presidential vote, an adjustment of this amount in their favor brings it to ~185 reasonably safe seats.

This leads us to our next point, which is whether using presidential lean underestimates the tendency for House Republicans to run ahead of the presidential vote, as happened in 2016 and 2020. While we readily agree that this may be true, it is worth noting that presidential and congressional votes are rapidly converging. With incumbency and spending acting as further complicating factors (Democrats tend to outspend Republicans now) and with very different districts drawn in many states, it is not readily clear that this downballot Republican boost will necessarily continue across the board for the remainder of the decade.

With that said, Split Ticket estimates that by presidential partisan lean, the House bias for 2022 will be around D+1. There are error bounds around this estimate, but the key point is that gerrymandering by itself is not likely to cost Democrats House control. Indeed, recent rulings have made it more likely than not that the House will have a slight Democratic bias for the decade, and we believe that there is a very substantial chance that this bias could manifest as early as 2022 in both the presidential vote and the overall House popular vote. 


If it’s not clear by now, redistricting will have huge implications on the political direction of the House over the coming decade. As our argument above outlines, Republicans may have to win the popular vote by at least a point in order to win the House. Given the national environment, a margin of R+1 or higher is far more likely than not for 2022, and we currently believe that Republicans will win the majority in November. But the slight Democratic House bias will probably start the chamber off at Leans Democratic in presidential years like 2024, as the median presidential environment is roughly D+2.

With House bias standing around D+1 and Senate bias clocking in at R+5, split control of Congress will probably be commonplace over the next few years. This reality, combined with the likelihood that polarization will cap House majorities at around 230 seats, might once again make gridlock more likely than not for the better part another decade. And so perhaps the old adage rings true once again: the more things change, the more they stay the same.

A special thanks to Ryan Brune, Andrew Ellison, @alexanderao, and @UMichVoter for their help with this piece, and to Noah Wyhof-Rudnick for the inspiration behind it.

A correction was issued on Monday, Feb. 7 at 1:25 PM EST — the figures in this article assume Alabama’s redistricting process goes 5R-2D because of the Supreme Court refusing to step in as of Monday. We have updated the figures in this article to revise our counts as necessary and address the uncertainty around the Black majority districts and the plausible plans in Pennsylvania, Florida, Alabama, and North Carolina.

I’m a software engineer and a computer scientist (UC Berkeley class of 2019 BA, class of 2020 MS) who has an interest in machine learning, politics, and electoral data. I’m a partner at Split Ticket, handle our Senate races, and make many kinds of electoral models.

My name is Harrison Lavelle and I am a political analyst studying at the College of New Jersey. As a co-founder and partner at Split Ticket, I coordinate our House coverage. I write about a variety of electoral topics and produce political maps. Besides elections, my hobbies include music, history, language, and fitness.

Contact me at @HWLavelleMaps or

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