Recently, Nick Stephanopoulos pointed out how Rucho was written as if constitutional racial vote dilution claims never existed. The same might also be said of the one-person, one-vote (OPOV) doctrine’s more complex (and seemingly forgotten) constitutional standard: “substantial equality.”

In Rucho, Roberts paints OPOV as the paradigm of simplicity, stating that it is “relatively easy to administer as a matter of math.” Rucho Slip Op. 20. Yet nothing could be further from the truth. Under the Equal Protection Clause, legislative districts must provide “substantial equality,” not strict population equality. As the Court stated in Mahan v. Howell, “so long as the divergences . . . are based on legitimate considerations incident to the effectuation of a rational state policy, some deviations from the equal-population principle are constitutionally permissible . . . .” 410 U.S. 315, 325 (1973) (quoting Reynolds v. Sims, 377 U.S. 533, 579 (1964)). In other words, it is not at all true that OPOV claims and partisan-gerrymandering claims are distinguishable on the basis that “it is illegal for a jurisdiction to depart from the one-person, one-vote rule,” as Roberts states in Rucho. Rucho Slip Op. 12.

Under the OPOV doctrine, legislatures can deviate from strict population equality in order to advance any number of legitimate state policies. The choice among (and balance between) these policies is left to the states themselves. Federal courts reviewing these decisions proceed in two steps.

First, they examine “whether it can be reasonably said that the state policy urged . . . to justify divergences . . . is, indeed, furthered by the plan adopted.” Mahan, 410 U.S. at 326. As part of this inquiry, courts have traditionally examined whether the policy urged has been applied inconsistently or in a discriminatory fashion. See Brown v. Thompson, 462 U.S. 835, 844 (1983) (accepting deviations from population equality that were “entirely the result of the consistent and non discriminatory application of a legitimate state policy”); Roman v. Sincock, 377 U.S. 695, 710 (1964) (permitting population deviations “only as may occur in recognizing certain factors that are free from any taint of arbitrariness or discrimination”). In other words, federal courts defer to the redistricting criteria and state policies advanced and adopted by the legislature, but check to make sure the population deviations actually advance those policies and that those policies are not being applied in an inconsistent, non-neutral manner. In Mahan, for example, Virginia wanted to maintain city- and county-boundaries, and the Court found that the deviations from population equality did, in fact, “advance the rational state policy of respecting political subdivisions.” 410 U.S. at 328.

Second, courts also examine “whether the population disparities among the districts that have resulted from the pursuit of th[e] plan exceed constitutional limits;” for a state policy, “however rational, cannot constitutionally be permitted to emasculate the goal of substantial equality.” Id. at 328, 326. This is by no means a clear-cut constitutional standard and evokes the same kind of “how far is too far” questions that supposedly make partisan-gerrymandering claims intractable. In Mahan, the Court upheld a 16.4% population deviation, noting that “[w]hile this percentage may well approach tolerable limits, we do not believe . . . Virginia has . . . sacrificed substantial equality to justifiable deviations.” Id. at 329. Indeed, the Court openly acknowledged in Mahan that “[n]either courts nor legislatures are furnished any specialized calipers that . . . establish[] what range of . . . deviations [from constitutional requirements] is permissible.” Id. The Court has never set out a clear percentage threshold for constitutional liability under the OPOV doctrine because that determination—whether a state has subordinated “substantial equality”—requires a delicate, case-specific judgment that turns on the facts on the ground and the specific policies advanced by the state.

This more honest and complex account of the OPOV doctrine demonstrates the ways in which Roberts’ superficial objections to the outlier method ring hollow. In Rucho, Roberts claims that the outlier method is “indeterminate and arbitrary” because “it does not make sense to use criteria that will vary from State to State and year to year as the baseline for determining whether a gerrymander violates the Federal Constitution.” Rucho Slip Op. 27-28. Roberts objects that “it is easy to imagine how different criteria could move the median map toward different partisan distributions” and that “the same map would be constitutional or not depending solely on what the map makers said they set out to do.” Id. But this is the same kind of fact-specific and deferential analysis that federal courts undertake in OPOV claims—allowing legislatures to articulate their own theory of representation and their own preferred criteria, but then calling legislators to account if they apply those criteria in a discriminatory fashion or if they go “too far” and subordinate “substantial equality.”

How has the Supreme Court avoided getting caught in constant political crossfire with such an amorphous and fact-intensive constitutional standard for OPOV liability? The Court also adopted an easily administrable burden-shifting standard: maps with population deviations above 10% are presumptively unconstitutional; maps with population deviations below 10% are presumptively constitutional. See Harris v. Ariz. Indep. Redistricting Comm’n, 136 S. Ct. 1301, 1307, 1310 (2016). Legislatures responded to this rule by steering well clear of the 10% threshold to avoid lawsuits even though the standard for constitutional liability remained as fuzzy and case-specific as ever. Maps could still be found unconstitutional below 10% or be found constitutional above 10%, but the burden-shifting threshold helped avoid constant litigation over the application of the constitutional standard itself.

This, too, shows Rucho’s supposedly “unanswerable question” (“how much is too much”) to be less daunting than portrayed. In rejecting the outlier method, Roberts asks “Would twenty percent away from the median map be okay? Forty percent? Sixty percent? Why or why not? . . . The Constitution provides no basis whatsoever to guide the exercise of judicial discretion. Common experience gives content to terms such as ‘substantial risk’ or ‘substantial harm,’ but the same cannot be said of substantial deviation from a median map. There is no way to tell whether the prohibited deviation from that map should kick in at 25 percent or 75 percent or some other point.” Rucho Slip Op. 28. Here, Roberts assumes that 20, 40, or 60 percent must be a constitutional standard of liability and finds no basis for drawing the line at any particular quantum.

But the OPOV doctrine demonstrates that there is no need for the presumptive line to be the same as the constitutional standard. The Supreme Court could have easily paired a clean and administrable burden-shifting rule with a more flexible but principled constitutional standard. For example, if a challenged district and challenged map fall within the majority of expected nonpartisan outcomes based on an outlier analysis, then the plaintiff could be required to show that it is more probable than not that illegitimate considerations predominated in the creation of the district.  If the evolution of the OPOV doctrine is any guide, legislatures would quickly move within the broad universe of maps that comply with the burden-shifting line, avoiding litigation over the more difficult constitutional question altogether and helping courts stay out of the fray and avoid being accused of picking winners and losers.

In fact, the Court’s holding in Rucho may well upset the uneasy truce that has helped the OPOV doctrine develop its reputation as “relatively easy to administer as a matter of math.” Rucho Slip Op. 20. After Rucho, state and federal courts alike might find themselves forced to answer a new question: How much pursuit of partisan advantage is permitted before it subordinates substantial equality? After all, if partisan advantage is now a “legitimate” redistricting policy in its own right (rather than a discriminatory application), then legislators may feel little need to continue operating within the OPOV doctrine’s clear 10% presumptive threshold and may begin re-exploring the limits of the more case-specific constitutional OPOV standard. Roberts’ attempt to extricate courts from the political fray in one area may have just made matters worse in another: federal courts might now be forced to answer, on a case-by-case basis, “how much” partisan advantage is allowed before the OPOV doctrine’s underlying standard is triggered. Will it be 17%? 20%? 25%? The Court may soon find itself forced to answer the very same “unanswerable questions” it was trying to avoid, just in a new context. The Court could have — and someday should — avoid all of this by (1) recognizing that partisan advantage cannot be considered a “legitimate state policy” under OPOV, and (2) implementing a burden-shifting standard for partisan outliers.

In the meantime, state supreme courts have the opportunity to learn from the U.S. Supreme Court’s oversight and incorporate the forgotten, nuanced nature of the OPOV doctrine into their decision-making calculus. If plaintiffs bring partisan-gerrymandering claims under state constitutional law and rely upon outlier methods, state courts should keep these doctrinal parallels, distinctions, and consequences in mind and should consider pairing a clear burden-shifting rule with a more case-specific constitutional standard. By doing so, courts might actually extricate themselves from the delicate business of regularly declaring “how much is too much.”