## Facts

- Colorado voters adopted a constitutional amendment (Amendment No. 7) altering legislative apportionment after pending federal challenges to prior apportionment.
- The amendment provided that the Colorado House of Representatives would be apportioned on a population basis.
- The amendment retained a Colorado Senate apportionment scheme based on a mix of population and non-population factors, including geography and historical divisions.
- Under the Senate plan, counties with about one-third of the state’s population could elect a majority of the Senate, and metropolitan areas with over two-thirds of the population could elect only a bare majority.
- The maximum population-variance ratio among Senate districts was approximately 3.6 to 1.
- Voters from the Denver metropolitan area alleged the Senate plan diluted their votes in violation of the Equal Protection Clause.
- A three-judge federal district court upheld the amendment, emphasizing its approval by statewide referendum, and dismissed the suit.
- The plaintiffs appealed directly to the U.S. Supreme Court.

## Issues

1. Whether the Equal Protection Clause permits a state to apportion one house of a bicameral legislature substantially on non-population factors that create major population disparities in representation.
2. Whether popular approval of an apportionment plan by referendum can validate a plan that otherwise dilutes individual voting power under the Fourteenth Amendment.
3. Whether, if one chamber’s apportionment is unconstitutional, the overall legislative apportionment scheme may be set aside where the provisions are not severable.

## Decision

- The Supreme Court reversed the district court and remanded.
- The Court held that both houses of a bicameral state legislature must be apportioned substantially on a population basis.
- The Court concluded the Colorado Senate plan departed too far from population-based representation to satisfy equal protection.
- The Court ruled that statewide voter approval of the plan did not cure the constitutional violation.
- Although the House apportionment was not directly challenged, the Court set aside the overall scheme because the Senate apportionment was not treated as severable from the House plan.

## Legal Principles

- The Equal Protection Clause requires that seats in both chambers of a bicameral state legislature be apportioned substantially according to population; only limited deviations are permissible for legitimate state objectives.
- Vote dilution caused by significant population disparities in representation constitutes invidious discrimination against voters in more populous areas.
- Majoritarian political processes, including referendum approval, cannot waive or override an individual’s federal constitutional right to cast a substantially equally weighted vote.
- When an unconstitutional apportionment provision is intertwined with the broader legislative apportionment framework, a court may invalidate the entire scheme rather than leaving a partial plan in place.

## Conclusion

The Court invalidated Colorado’s voter-approved legislative apportionment because the Senate’s structure gave substantially unequal weight to votes across counties, reaffirming that both legislative chambers must be apportioned mainly by population and that popular ratification cannot excuse unequal representation under the Fourteenth Amendment.


Lucas v. Forty-Fourth Gen. Assembly of Colo., 377 U.S. 713 (1964)