Supermajority gerrymandering

This variant of a major bug in democracy gives supermajority power to a minority of voters

Tomorrow a Tennessee court takes up the question of whether the state’s legislative districts are gerrymandered. The districts there are drawn in a way that disfavors minority voters, eliminates competition, and overall may form an exotic phenomenon, a supermajority gerrymander. This and a second supermajority gerrymander in Wisconsin have created recent political havoc.

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In American democracy, a critical feature is the ability of one branch of government to restrain the excesses of another branch. But gerrymandering provides a way to evade this essential principle - without having to amend the constitution. The result is a government that is almost totally unmoored from the voters it is supposed to serve. 

State legislatures and governors are expected to work together. The governor has the power to sign or veto a bill passed by the legislature. But a supermajority, usually two-thirds of the legislators, can override the governor’s veto. In this way they can bypass a governor who is out of step with consensus opinion. The implicit assumption is that a supermajority is more likely to represent the consensus. But what if that isn’t true?

Condemnations of partisan gerrymandering often focus on the threat that a minority of voters can elect a legislative majority. Today’s focus is on an advanced maneuver for true Zen masters: arranging matters so that a minority can even elect not just a majority, but a supermajority. The resulting supermajority, immune from public opinion, can engage in extreme behavior without paying a price in terms of political power.

The basis for electoral impunity in Wisconsin and Tennessee is gerrymandering built on a foundation of partisan polarization. Because nearly everyone votes the same way from election to election, a district with a margin between the two parties of more than 7 points is generally safe for the favored party. Resources like the Princeton Gerrymandering Project or the excellent and universally used Dave’s Redistricting App can show the likely performance of a map.

Wisconsin’s engineered supermajority

Consider the Wisconsin Senate. The election to the state Supreme Court of Janet Protasiewicz. Protasiewicz’s win ensures that the Court will be taking a hard and close look at the legality of the state legislative map under which the state Senate was elected. That same Senate has made noise about impeaching and convicting her for an unspecified offense. (Unfortunately for those suggesting this gambit, the likeliest consequence of a conviction would be that Governor Tony Evers’s chosen replacement would leave the court with the same ideological balance.)

The Wisconsin Senate has 33 seats. Despite the fact that the state’s vote splits 50%-50%  in Dave’s Redistricting App, 20 seats are safe for Republicans and 9 seats are safe for Democrats, leaving only 4 swing seats. In 2023, the swing seats split equally to give a 22-11 chamber - a veto-proof majority. 

This lopsided outcome did not arise naturally. The People’s Commission Senate map, which the legislature disregarded, had 14 safe Republican seats, 12 safe Democratic seats, and 7 swing seats, and received an “A” from the Princeton Gerrymandering Project. Using it as a benchmark, we can illustrate the extremeness of the enacted map.

This chart shows what vote would be necessary to get a majority or supermajority.

The Senate has a remarkably low vote threshold to attain a legislative majority, 44.1% Republican. The threshold is even lower, 43.4%, in the Assembly, whose districts are based on Senate districts. These numbers are farther from 50% than any other swing state. In short, by the criterion of antimajoritarianism, Wisconsin’s legislature is the most gerrymandered in the nation.

But here is an even more amazing calculation. To reach a Senate supermajority, Republicans only need 47.5% of the statewide vote - still several points short of a majority. This advantage is highly asymmetric: to get a supermajority, Democrats would need 11 points more, or 58.4%.

The practical upshot is that even without a majority of voter support, Republicans can easily hold both chambers of the legislature and even a Senate supermajority - enough to impeach and convict officials in other branches of government. The state Supreme Court is the only bulwark against such conduct.

Supermajority insurance in Tennessee

But now the Tennessee House has stolen the spotlight from Wisconsin. By a two-thirds vote, the Republican-controlled chamber ejected two Black Democrats for violating decorum on the floor via their loud support of pro-gun-regulation protesters. Partisan statehouse politics in Tennessee has been nasty for some time, but the ejection of the lawmakers was widely seen as a new low, enough to make national headlines.

Unlike Wisconsin, Tennessee is a strongly Republican state, with an average 61%-39% statewide vote advantage over Democrats. Because of this, gerrymandering in Tennessee is easily overlooked by national analysts since there’s no question about which party ought to have the legislative majority. But this overlooks redistricting’s potential power to build and preserve a supermajority.

Republicans had single-party control of the redistricting process. In the enacted map, of the 99 current Tennessee House districts, 72 are safe Republican, 20 are safe Democratic, and 7 can go either way. This pattern guarantees a comfortable Republican supermajority.

We can see how this feat was accomplished by looking at the map in Dave’s Redistricting App. In this example, the area around Memphis is drawn in a manner that packs voters into a handful of districts that are 61% to 82% Black, minimizing their total representation, while carefully configuring nearby Districts 50, 59 and 60 to be competitive.

Similar jiggery-pokery packed or split Black communities in Nashville, Jackson, Clarksville, Chattanooga, and Knoxville. Because voting in Tennessee is strongly racially polarized, this reduces representation of Democrats.

What would a more balanced process produce? Rather than draw a single map, which is reliant on detailed judgments, I took a resampling approach similar to my NYT piece on the Great Gerrymander of 2012. I collected district-level partisan breakdown of legislative districts across many states, then calculated what fraction of them would be safe or competitive given Tennessee’s partisan makeup. That calculation gives 65 safe Republican seats, 24 safe Democratic seats, and 10 swing seats. In such a map, Democrats would have the potential in a strong year to block a 66-seat supermajority. The potential effect of Tennessee’s gerrymander on the state’s politics is pernicious. Under the current map, legislators are safe in taking risks that would normally get at least some of them ejected from office, the ejection of legislators being just one example of multiple scandals and controversies there.

One caveat to this approach is that it does not capture the specifics of a state’s partisan geography. Tennessee has extremely strong geographic polarization, which makes it hard to avoid drawing strongly partisan Republican and Democratic districts. Drawing a map that achieves what the simulations suggest may require focused effort.

Manipulating supermajorities across the nation 

We can now generalize this approach to other states to identify when a majority party has drawn a map that works to insulate its supermajority from popular opinion.

I estimate that under party-blind districting, Republicans would generally need 58.6% of the vote to guarantee a two-thirds supermajority, and Democrats would need 60.7% of the vote to gain themselves such a supermajority. This slight difference of two points is likely to arise from the higher density of Democrats in urban districts compared with a high but not overwhelming density of Republicans in rural districts. 

I examined 12 states. To see the results, steel yourself for a complicated diagram...

Here’s how to read this diagram. The horizontal lines indicate the threshold vote needed for a supermajority. On the left are states where Republicans controlled the process. In Wisconsin, Tennessee, Wisconsin, Kansas, they drew maps to lower the necessary threshold. The exceptions were Georgia and Texas.

The actual estimated vote shares are indicated by the black circles. Gerrymandering appeared to be necessary for reaching a legislative supermajority in three states: for Republicans, Wisconsin and almost North Carolina (the last little bit was achieved last week when one Democrat defected to Republicans, giving them a supermajority).

In addition, Tennessee is quite amazing. Although an 11% shift in the vote is highly unlikely, if it were to ever occur, as little as 49.5% of the statewide vote would be enough to still elect a supermajority. It is nearly as bad as Wisconsin.

Democrats are not immune to this temptation. Gerrymandering is likely to have brought about supermajorities in Nevada and Illinois. And similar to Tennessee, Massachusetts was already likely to elect a supermajority under a neutrally-drawn map, but a gerrymander makes their margin voter-proof.

Finally, one pleasing contrast. In states where a commission drew the maps on a bipartisan basis, the threshold for a supermajority is quite high. In Arizona, Michigan, and Pennsylvania, the vote needed to reach a supermajority (here plotted as Democratic votes) is 58-62%, very close to the result of my resampling calculation. This suggests that a process in which the legislature is not involved, the natural outcome is met - and presumably the intent of state constitutional framers.