In a (barely) 11 page opinion the Supreme Court did what three lower court judges could not do in three separate opinions: agree.  

In Harris v. Arizona Independent Redistricting Commission the Supreme Court confirms that state and local governments don’t have to apportion legislative districts perfectly, but they do need a good reason for failing to doing so. But we knew that before. 

The Court held unanimously that Arizona’s redistricting plan, which had a total population deviation among districts of 8.8 percent, wasn’t unconstitutional. Those attacking the plan failed to show it is more probable than not that the deviation reflects illegitimate reapportionment considerations.

Initially, the maximum population deviation between the most populated districts and least populated districts in the state legislative redistricting plan, which was based on a grid-like map, was 4.07 percent. Section 5 of the Voting Rights Act (VRA) requires that redistricting plans in “covered” jurisdictions don’t worsen the position of minority voters. All the commissioners agreed that to obtain preclearance from the Department of Justice (DOJ) under the VRA, Arizona’s plan had to contain at least 10 districts where minority voters are able to elect their candidate of choice.

DOJ does not tell states and local governments how many “ability-to-elect” districts are required or how they are calculated. A majority of the commissioners agreed to keep a higher population of minority voters in District 8, which leans Republican, so that the Commission might be able to claim District 8 was an 11th “ability-to-elect” district. The population deviation in the final plan was 8.8 percent.

Per one-person, one-vote legislative districts much be roughly equal in population. But if population deviations are less than 10 percent those attacking the plan must show that it is more probable than not that the deviation “reflects the predominance of illegitimate reapportionment factors rather than the ‘legitimate considerations,’” like compactness and contiguity. 

A group of Arizona voters claimed that the deviations from “absolute equality” reflect the fact that the Commission was trying to help the Democratic Party by making changes to District 8. The Court assumed, but did not decide, that partisanship is an illegitimate redistricting factor. Regardless, the Court concluded that the deviations predominately reflected the Commissions efforts to comply with the VRA, not to help a political party. 

Additionally, the Court agreed that it was likely that almost all the Democratic-leaning districts in Arizona are somewhat underpopulated and almost all the Republican-leaning districts are somewhat overpopulated. But this reflects the fact that minority voters disproportionally favor Democrats and that Arizona was trying to maintain at least 10 “ability-to-elect” districts. Finally, while Section 5 of the VRA is currently inoperable due to Shelby County v. Holder (2013), that case was not decided in 2010 when the Commission’s plan was created. So the Commission properly tried to comply with Section 5.