Evenwel v. Abbott

The equal protection principle of “one person, one vote” permits States to apportion legislative districts using total population, and does not mandate that districts be apportioned based upon registered or eligible voter population.

Baker v. Carr, 369 U.S. 186, established the one person, one vote principle to protect the fundamental right to vote from vote dilution by malapportionment. States districting plans are in compliance if the maximum population deviation between the largest and smallest districts is less than 10%. In 2013, the Texas legislature adopted a plan for apportionment of Texas state senate districts which grew out of federal court Voting Rights Act pre-clearance litigation and which complied with the 10% total population standard. Petitioners, who live in a senate district with an unusually large number of registered or eligible voters, contend the use of the total population, instead of registered or eligible voter populations for legislative apportionment, diluted their right to vote as it revealed disparities in district size exceeding 40%. The Court relied upon history, precedent, and practice to hold that States may measure compliance with the one person, one vote principle by relying upon the total population of state and legislative districts. The Court did not address whether a State that changes its distrincting plan to one that is based on registered or eligible voters would satisfy the one person, one vote principle.