The one-person, one-vote rule requires states and local governments to draw congressional districts with populations as close to perfect equality as possible. Recently, in Evenwel v. Abbott, 578 U.S. ___ (2016), the United States Supreme Court held states and local governments may apportion state legislative districts based on total population. The Evenwel decision confirmed that jurisdictions are permitted to deviate between the largest and smallest district by less than 10%. Maximum population deviation is defined as the sum of the percentage deviations from perfect population equality of the most- and least- populated districts.

After the 2010 census, the Texas Legislature redrew its state senate districts based on census total population data so that each district included roughly an equal number of people. The districts contained a different number of eligible- and registered-voters. The maximum total-population deviation between districts was about 8%, whereas the maximum eligible-voters deviation between districts exceeded 40%. The Court noted that all states use total-population data when designing congressional and state-legislative districts.

Voters (“Evenwel”) living in districts with particularly large eligible-voter popula­tions sued Texas in the U.S. District Court for the Western District of Texas, contending that basing apportionment on total population dilutes their votes in relation to voters in other districts, in violation of the one-person, one-vote principle of the Equal Protection Clause. The District Court dismissed their complaint, concluding that jurisdictions may use any neutral, nondis­criminatory population baseline, including total popula­tion, when drawing state and local legislative districts. Evenwel appealed directly to the United States Supreme Court.

The United States Supreme Court unanimously affirmed. In delivering the Court’s opinion, Justice Ruth Bader Ginsburg first spoke to the history of the “one-person, one-vote” principle. In Reynolds v. Sims, 377 U.S. 533 (1964), the Court established the principle of “one-person, one-vote,” holding that the Equal Protection Clause requires that legislative districts be apportioned equally so that votes would have equal weight. After examining the constitutional history and the Court’s past decisions, the Court concluded “that districting based on total population serves both the State’s interest in preventing vote dilution and its interest in ensuring equality of representation.”

Finally, the Court emphasized adopting voter-eligible apportionment would upset a well-functioning approach to districting that all 50 states and countless local jurisdictions have followed for decades, and Evenwel failed to show the Court why it should disturb the longstanding use of total population. The Court noted that representatives serve all residents, not just those eligible or registered to vote. The Court concluded the Texas map complied with the requirements of the on-person, one-vote principle.

Interestingly enough, Texas argued that jurisdictions may design districts using any population baseline, including total population and voter-eligible population, so long as the choice is rational and not invidiously discriminatory. The Court did not address this issue, and it seems that the Court will not address it until a state or local government decides to divide districts based on voter-eligible population.

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