In Smith v. Allwright, Thurgood Marshall rose in front of the United States Supreme Court to argue that Texas’s Democratic primary system allowed whites to structurally dominate the politics of the one-party South. Specifically, the case presented the question of whether the Texas Democratic Party’s policy of prohibiting Blacks from voting in primary elections violated the Fourteenth and Fifteenth Amendments.
The Supreme Court held that it did, explaining that:
The United States is a constitutional democracy. Its organic law grants to all citizens a right to participate in the choice of elected officials without restriction by any state because of race. This grant to the people of the opportunity for choice is not to be nullified by a state through casting its electoral process in a form which permits a private organization to practice racial discrimination in the election.
In so ruling, Smith overruled a unanimous nine-year-old decision in Grovey v. Townsend that held that the Texas Democratic Party’s race-based restrictions on voting in primaries was constitutional because it was not state action, and thus it had not been endorsed or authorized by the state.
It was the watershed in the struggle for Black rights, and it signaled the beginning of the Second Reconstruction and the modern civil rights movement. The political and social advances of Blacks simply could not have occurred without the changes that came in the wake of the overthrow of the Democratic white primary.
Marshall characterized the ruling of Smith, which he considered his most important case, as “so clear and free of ambiguity” that the right of Blacks to participate in primaries was established “once and for all.”
African-American voter registration vastly improved immediately following the Court’s ruling in Smith, causing Marshall to recognize the case as “a giant milestone in the progress of Negro Americans toward full citizenship.”
The number of Southern blacks registered to vote rose to between 700,000 and 800,000 by 1948 and then to one million by 1952.
At the same time, Marshall cautioned that the work of ridding the country of racial discrimination in voting and other areas was not complete and foreshadowed the ruling in Brown v. Bd. of Education:
The collapse of the white Democratic primary, despite fond hopes, has not resulted in full participation by all in the political life of the South. But the story of the struggle to overcome this barrier is particularly meaningful today. For, if nothing else, it indicates the fate which awaits the ‘legal means’ which some of the Southern states have drafted to preserve segregated schools.
 Pamela S. Karlan, Ballots and Bullets: The Exceptional History of the Right to Vote, 71 U. Cin. L. Rev. 1345, 1356 n.69 (2003) (citing Alexander Keyssar, The Right to Vote: The Contested History of Democracy in the United States 248 (2000)).