The Supreme Court in a short, unanimous opinion by Justice Breyer, has rejected challenges to Arizona’s state redistricting done by commission. The Court held that it is permissible to deviate from perfect population in drawing state legislative district lines (generally by up to 10 percent) and that the commission did not engage in a partisan gerrymander. This is the second time within a year the Court has addressed something to do with the commission; last year (in Arizona Legislature v. Arizona Independent Redistricting commission) the Court held it was permissible for the Commission to draw congressional district lines in a procedure approved by voter initiative even though the Constitution gives the state “legislature” the right to pick the rules for congressional elections.

Today’s opinion in Harris v. Arizona Independent Redistricting Commission is significant in a few ways: First, it mostly restores the 10 percent safe harbor, which gives those drawing districts greater flexibility in drawing district lines (and, though the Court doesn’t say it, more opportunity to play partisan games with under- and over-population). Only in unusual, egregious cases will this amount of deviation giving rise to a successful constitutional lawsuit. Second, the Court almost holds that compliance with the Voting Rights Act’s section provides a good reason to deviate from perfect equality. Third, by writing a minimal opinion that decided only what was necessary, the Court was able to avoid a 4-4 split even though there are some great disagreements on larger issues among the Justices. (Justice Thomas, for example, does not even believe the Voting Rights Act should apply to section 2 vote dilution claims, and Justices Roberts, Alito, and Kennedy have been very skeptical of strong readings of the Voting Rights Act.) More flexibility for line drawers can be a double edged sword.

The question of deviation from perfect numerical equality in drawing district lines had seemed until the 2000s like it was set at a 10 percent safe harbor, with more if there was a good reason. But many read the summary affirmance in the 2004 Larios decision as not allowing for deviations even within the 10 percent safe harbor when it is done for partisan purposes. In today’s Harris v. Arizona Independent Redistricting Commission case,  the Court distinguished, but did not overrule, Larios:

Second, the appellants point to Cox v. Larios, 542 U. S. 947 (2004), in which we summarily affirmed a district court’s judgment that Georgia’s reapportionment of representatives to state legislative districts violated the Equal Protection Clause, even though the total population deviation was less than 10%. In Cox, however, unlike the present case, the district court found that those attacking the plan had shown that it was more probable than not that the use of illegitimate factors significantly explained deviations from numerical equality among districts. The district court produced many examples showing that population deviation as well as the shape of many districts “did not result from any attempt to create districts that were compact or contiguous, or to keep counties whole, or to preserve the cores of prior districts.” Id., at 949. No legitimate purposes could explain them. It is appellants’ inability to show that the present plan’s deviations and boundary shapes result from the predominance of similarly illegitimate factors that makes Cox inapposite here. Even assuming, without deciding, that partisanship is an illegitimate redistricting factor, appellants have not carried their burden.

The Court also came close to holding it is permissible to deviate from perfect mathematical equality to comply with the Voting Rights Act. It noted in the past that some Justices have held underpopulation is allowed in drawing districts to ensure under section 2 of the Act that minority voters have an equal opportunity to participate in the political process and to elect representatives of their choice. (It doesn’t look like the Court directly holds that in this case, as it is not necessary to the decision.) And it held that Arizona could have deviated from perfect equality to comply with Section 5 of the Act, which the Court later gutted in the 2013 Shelby County case. It rejected the idea that because of the later Shelby case, reliance on Section 5 becomes suspect.

Finally, the Court rejected the idea that this was a partisan gerrymander, obliquely recognizing the race or party question. Sure it was Democratic districts that were underpopulated, but that was because minority voters in Arizona tend to vote for Democrats:

The appellants make three additional arguments. First, they support their claim that the plan reflects unreasonable use of partisan considerations by pointing to the fact that almost all the Democratic-leaning districts are somewhat underpopulated and almost all the Republican-leaning districts are somewhat overpopulated. That is likely true. See 993 F. Supp. 2d, at 1049 (providing a chart with percentage deviation figures by district). But that fact may well reflect the tendency of minority populations in Arizona in 2010 to vote disproportionately for Democrats. If so, the variations are explained by the Commission’s efforts to maintain at least 10 ability-to-elect districts. The Commission may have relied on data from its statisticians and Voting Rights Act expert to create districts tailored to achieve preclearance in which minority voters were a larger percentage of the district population. That might have necessitated moving other voters out of those districts, thereby leaving them slightly underpopulated. The appellants point to nothing in the record to suggest the contrary.

Finally, the Court imposed a difficult to meet test for showing when deviation from the 10 percent safe harbor is impermissible:

In sum, in a case like this one, those attacking a state-approved plan must show that it is more probable than not that a deviation of less than 10% reflects the predominance of illegitimate reapportionment factors rather than the “legitimate considerations” to which we have referred in Reynolds and later cases. Given the inherent difficulty of measuring and comparing factors that may legitimately account for small deviations from strict mathematical equality, we believe that attacks on deviations under 10% will succeed only rarely, in unusual cases. And we are not surprised that the appellants have failed to meet their burden here.

[This post has been updated.]