How Democrats learned to love gerrymandering to avoid a biased House map in redistricting

The grinding battle over congressional redistricting is drawing to a close. And, contrary to expectations that the process would result in big Republican gains, the final House of Representatives map may well improve somewhat for Democrats.

The main reason is gerrymandering — redrawing of district lines for partisan benefit. Republicans built on their existing gerrymanders to try to expand their House advantage, but Democrats fired back even more powerfully with gerrymanders of their own.

Basically, Democrats saved themselves by resorting to a tactic they’ve previously denounced as not only unfair but downright unethical — House Speaker Nancy Pelosi called gerrymandering “unjust and deeply dangerous” in 2019. But in the absence of national reforms banning the practice, refusing to gerrymander would have meant effective unilateral disarmament, ceding the GOP a significant advantage in the battle for control over the House.

Redistricting has proceeded like a tug of war. As state legislatures, judges, and commissions have approved new maps, creating more safe or swing districts in various states, the underlying partisanship of the median House district has been pulled in one direction, and then the other. The most powerful pulls came from either state legislatures that gerrymandered, or state courts that struck down certain gerrymandered maps, as this graphic shows:

Amanda Northrop/Vox

This cycle’s Republican gerrymanders pulled the median district (which already leaned 2 percentage points to the right) another point further right. But state court rulings striking down North Carolina and Ohio maps effectively wiped out most of that net gain.

Meanwhile, Democratic gerrymanders in states like New York and Illinois pulled the median district nearly 3 points leftward, so it was actually close to neutral. (Joe Biden’s margin in the median district would have nearly matched his national popular vote margin in the 2020 presidential election.) But an aggressive gerrymander in GOP-controlled Florida could soon shift things right again, if approved. Other state court rulings could shift things further, particularly in New York, where Democrats’ gerrymander is under scrutiny.

Currently, it looks like there will be close to an equal number of districts leaning left and right of the national average, with a slight edge to Republicans in the median district.

Now, it’s entirely possible, perhaps likely, that Democrats will still lose badly in House elections this fall — the party has a small majority, President Biden is unpopular, and the historical pattern is for the incumbent’s party to struggle in the midterms. But unlike much of the previous decade, the underlying map may be at least somewhat less biased in Republicans’ favor.

How Republicans won a big gerrymandering advantage a decade ago, then saw it shrink

The last national redistricting happened after Republicans won sweeping victories in the 2010 midterms, giving them control over many state legislatures and governorships. They used that power to draw lines that gave them a big advantage in the House.

By 2012, when that last redistricting was finished, the median House district leaned nearly 6 percentage points further toward Republicans presidentially than that year’s national popular vote. The results were clear: Obama won nationally by about 4 points in 2012, but he lost the median district by about 2 points. What’s more, 55 percent of the overall House districts (240 out of 435) leaned Republican, per the New York Times. That sizable advantage helped Republicans hold the House in 2012 despite Obama’s national win.

But over the course of the ensuing decade, that GOP advantage significantly eroded. Changes in demographic voting patterns made many suburban districts less safe for Republicans. Meanwhile, courts struck down Republican gerrymanders in states like Florida, Pennsylvania, and Virginia. By the time the 2020 results were in, the median House district still leaned toward Republicans, but only by 2 points, rather than 6 points. And about 52 percent of districts (228 out of 435) had a Republican lean.

That was real progress for Democrats on reducing the bias of the House, but it was accompanied by disappointment. First, though Democrats performed well in the 2018 and 2020 elections, they fell short of retaking several key governorships and legislatures, meaning Republicans would have the power to gerrymander again in these states. Second, the party had hoped the Supreme Court would declare partisan gerrymandering unconstitutional, banning it nationwide, but Trump’s appointees moved to the court to the right and the conservative majority ruled otherwise. Third, efforts to pass a nationwide gerrymandering ban through the Democrat-controlled Congress under Biden were stymied by the Senate filibuster.

So as 2021 began, Republicans had the power of line-drawing in several swing states, as well as red states where they hadn’t yet maxed out their advantage. The GOP still had an advantage in the House map, and now it seemed they could entrench and expand it.

How to measure a district’s partisanship

There are varying ways to estimate the underlying partisanship of a district or an overall map, but for now, I’ll focus mainly on a simple one: how the district voted in the most recent presidential race, compared to the national popular vote. (The New York Times’s Nate Cohn used this metric in his own recent analysis.)

In 2020, Biden won the popular vote by a margin of 4.4 percentage points. If he won by more than that in a given district, I’m calling that a Democratic-leaning district. If he won by less than that, or lost the district, I’m calling it a Republican-leaning district. This metric lets us look at the partisan lean for the median House district (the one necessary to give a party a majority), and also measure how many districts lean toward Democrats or Republicans overall.

Focusing on the presidential numbers won’t be a perfect guide to House results. House candidates run with their own strengths and weaknesses, and some manage to defy their districts’ underlying partisan lean. But there have been fewer such candidates lately — in 2020, only 16 out of 435 House victors won a district where the opposite party’s presidential candidate also won.

Other analysts may have slightly different specific calculations for the map’s overall lean. For this cycle, I’ve used the Cook Political Report (an invaluable resource for anyone closely following elections), which calculated the presidential results in each new district. As an alternative, Cook also uses a metric called the PVI (Partisan Voting Index), which incorporates the past two presidential elections. FiveThirtyEight has its own “partisan lean” score. The Economist’s G. Elliott Morris argues it can be most predictive to look at the presidential election prior to the most recent one. Still, these different estimates will probably be roughly similar overall.

The Republican gerrymanders of 2021-2022

Let’s start by looking at how Republican gerrymandering attempts fared this cycle. The GOP did indeed try to expand their advantage in key states, but their overall impact was hampered by a few factors.

• North Carolina was most painful for Republicans, as the state supreme court struck down their sweeping gerrymander and replaced it with a relatively balanced plan.
• An unfavorable court ruling in Ohio also knocked down another sweeping GOP gerrymander, but the party came back with an only slightly less gerrymandered map that the court will apparently allow to be put in place this year.
• In Texas, where the preexisting GOP gerrymander was weakening due to changes in voting patterns such as suburbs trending Democratic, the GOP made a strategic decision to focus on maximizing safety for incumbents rather than expanding their reach. So they wiped out most swing districts in the state and Republican incumbents will be harder for Democrats to defeat, but the number of districts that voted more for Trump than the national average in 2020 is staying the same (25 out of now 38 in the state, a major Republican advantage in a state Trump only won by 5.6 percentage points).

In the finalized maps so far, then, Republicans have ended up with just a handful of new districts leaning in their favor. But that’s compared to a map that was already favorable to them, and they managed to preserve or strengthen preexisting pro-GOP maps in key states.

However, one other state may soon give them a big assist: Florida Gov. Ron DeSantis (R) and GOP state legislative leaders have been at odds for months on just how much the House map should tilt in Republicans’ favor, with DeSantis pushing for a more extreme gerrymander. And just this week, DeSantis appeared to win: The…