Dilution is a scientific term for dissolving a substance and weakening it by spreading it out, like dropping salt into water. Voter dilution spreads a geographically close minority group out through a political unit to lessen the strength of the votes of its members.

But people who share a minority characteristic are not assumed to be a monolith, so the Supreme Court has set specific guidelines to determine whether an at-large voting system, for example, actually dilutes the voice of racial minorities. Thornburg v. Gingles (1986) held that, for dilution challenges to at-large voting systems under the federal Voting Rights Act (VRA), a challenger must show that (1) the group is “politically cohesive” in addition to being a minority, (2) the group is large enough and compact enough that it would form the majority in a single voting district, and (3) that the majority group votes in a bloc that usually defeats the minority group’s preferred candidate. Bartlett v. Strickland (2009) reinforced that framework, leaving us with an interpretation of the VRA that protects individuals’ rights to vote but does not create proportional representation for groups.

California passed its own Voting Rights Act to eliminate the geographical requirement. Under the CVRA, challenges to at-large voting merely need only show that polarized voting occurs on majority-minority lines—and then the at-large election must be replaced with a district map that ensures minority representation. For geographically dispersed groups, this mapping implicitly requires gerrymandering based on the minority characteristic. Additionally, cities must pay a challenger’s legal fees if they lose one of these challenges, unless they immediately abandon at-large voting after being informed that a group intends to sue.

But in California voter dilution exists any time a minority group tends to disagree with the majority on electoral matters; like finding a glass of sea water, the salt may be diluted but no dilution occurred. The City of Poway, like dozens of California municipalities, was threatened with a vote dilution lawsuit under the CVRA and abandoned its at-large electoral system of selecting city council members that it had used since its founding in 1980.

Don Higginson, a Poway voter, challenged the new district map, and the constitutionality of the CVRA. The district court dismissed his complaint and the U.S. Court of Appeals for the Ninth Circuit affirmed the dismissal. He now seeks Supreme Court review. The Cato Institute joined the Pacific Legal Foundation and four other organizations on an amicus brief in support of Higginson’s petition, arguing that the CVRA’s dilution provisions violate the Equal Protection Clause of the Fourteenth Amendment and go beyond the limits of what Supreme Court precedent allows in terms of the use of race in drawing election districts.