This week the Supreme Court prepared to make voting rights history ahead of the 2020 Census redistricting cycle. Justices heard oral arguments in two partisan gerrymandering cases: a Republican gerrymander in North Carolina (Rucho v Common Cause) and a Democratic gerrymander in Maryland (Lamone v Benesik). Plaintiffs in these cases are seeking relief and a standard to rein in state legislative attempts to maximize partisan advantage through the manipulation of district boundaries.
Oral arguments laid out in unusually clear fashion why these difficult questions have left the Justices grappling for answers. Taken together, the arguments create a frottage that reveals fundamental limitations on the fit between constitutional protections and our electoral institutions.
Why the obsession with proportional representation?
During both cases a lot of time was spent discussing whether the standard for a fair partisan map is proportional representation, or a close correspondence between the share of votes a party earns statewide and the share of legislative seats it wins. At one point in an exchange with Mr. Kimberly (representing Maryland plaintiffs) over the fairness of a 5/3 Democratic/Republican split, Justice Kavanaugh claimed “that shows…the overwhelming driver is proportional representation…Do you think the Constitution requires proportional representation or something close to proportional representation?”
After Mr. Kimberly responded that he did not see a textual indication in the Constitution, Justice Kavanaugh gets more specific:
Kavanaugh: “Equal Protection Clause does not suggest to you something where political groups are treated roughly equally?”
Kimberly: “Your Honor, if that’s the way that you’re inclined to think about it, I’m certainly…
Kavanaugh: “No I’m just asking why…”
Kimberly: “Happy to have you rule that way.” (Court breaks out in laughter.)
Kavanaugh: “…challenging the maps but running away from proportional representation, even though…there’s a suggestion that really it all comes back to proportional representation in some respects.”
There is one respect under which equal protection, or political equality, does require proportional representation. Not as a matter of what the Constitution says, but as a matter of fact. That is, the only electoral system that gives exact equal value to every voters’ party preference is pure proportional representation, where those preferences are reflected perfectly in the percentage of seats that each party wins.
So on the one hand, it is a fact that equal treatment under the law is truly maximized only under proportional electoral systems, where every vote contributes to seat shares. On the other hand, the law currently prohibits the use of proportional electoral systems for Congressional elections, and as Justice Kavanaugh later reminds Mr. Kimberly: “Justice O’Connor and Justice Kennedy have made very clear in various opinions that the Constitution contains no such guarantee.” As currently interpreted, whatever the Constitution requires falls short of proportional representation.
A standard fit for a district?
The lower equality standard reflected in current Constitutional interpretations is well understood among both election law experts and political scientists. Justice Breyer has noted the tension between single-seat districts and proportional representation. The most prominent metric of partisan advantage in political science, Gelman and King’s partisan asymmetry statistic, is a measure of vote dilution that accounts for disproportionalities inherent in our single-seat, winner-take-all elections. Asymmetry measures the difference in seat shares that each party’s voters receive in a plan for the same statewide vote share, say 50%. A second component of the Gelman and King model, responsiveness, captures that inherent disproportionality that emerges when voters shift support from one party to another, typically resulting in a “winner’s bonus.” A system that is less responsive to shifts in support is evidence of a more durable gerrymander.
As responsiveness decreases (the slope flattens), a party’s share of seats can withstand more loss of voter support. Lack of responsiveness is evidence of a durable partisan gerrymander.
And it is within this asymmetry framework that we find a test that parallels the three-prong approach established for deciding racial gerrymandering cases in Thornburg v Gingles. It is described in the Amicus Brief submitted in the North Carolina case (in favor of neither party) by professors Bernard Grofman and Keith Gaddie. Their proposed test requires that plaintiffs first demonstrate that the opposition party has been deprived of partisan advantage in at least one district in the enacted plan in the same manner as Gingles: targeted voters must be a large and compact enough group to create a majority district without diluting their advantage in other districts. Second, the opposition voters must exhibit polarized partisan voting. Voters who regularly shift support between parties would not provide an advantage to either.
Third, plaintiffs must demonstrate vote dilution at the district level, through either a district where the opposition party regularly loses, or in a majority district where voters could be allocated more efficiently across districts. Finally, because changing parties is an option whereas changing race is not, the responsiveness statistic can be used to demonstrate the durability of a partisan gerrymander.
Justice Kagan’s expressed concern that the Maryland plan “flips the composition of the district from 47 percent Republicans and 36 percent Democrats to, instead, 45 percent Democrats and 34 percent Republicans, effectively ensuring that Republicans will never win this seat again…” and is excessive can be answered by including durability in the test.
Using responsiveness as a means of estimating durability is especially appealing as it is distinct from proportional outcome expectations. In fact, this final element of the test could require that very disproportional plans be upheld. Consider an extreme hypothetical where the difference in party affiliation in Maryland’s eight districts is only one person in each district. That is, each district is nearly perfectly split 50/50. In such a case, one person changing their vote changes control of the district, and if each pivotal voter in the district votes Democratic, Democrats win all eight seats, which is the least proportional plan. However, responsiveness is also maximized if it only takes eight people to flip every district, demonstrating that the plan is not a durable gerrymander.
Finding asymmetry demonstrates that one party’s voters are experiencing vote dilution at the state level. This partisan gerrymandering test goes further to identify where the dilution is occurring, how durable it is, and how a remedy would change an existing map. The constitutional logic is parallel to what has been long established and upheld in racial vote dilution cases.
Chief Justice Roberts pointed out that the extent of gerrymandering has changed. Justice Kavanaugh acknowledged that partisan gerrymandering is a problem for democracy. Could a majority of justices recognize that this court’s legitimacy depends, at least in part, on its ability to prevent partisan interests from dictating electoral outcomes at the expense of voters? They have a remedy. It won’t solve the problem of political inequality in all elections, but it is probably the best we can do with what we have. If what we have is worth saving, it is imperative that the Court act.