In the case of Watson, Attorney General of Florida, et al. v. Buck et al., 1940, the U.S Supreme Court ruled in favor of Buck and his fellow plaintiffs who were African American voters from Florida. The plaintiffs had filed a suit against state officials for denying them their right to vote in primary elections based on their race which was contrary to the Fifteenth Amendment that prohibits racial discrimination in voting rights. The court held that although political parties are private entities and can choose members as they wish, when it comes to public functions like primaries where nominees are selected for general elections, they must adhere to constitutional standards prohibiting racial discrimination. Therefore, excluding black citizens from participating in these primaries violated their constitutionally protected voting rights.

In the dissenting opinion for Watson, Attorney General of Florida, et al. v. Buck et al., Justice Hugo Black argued that the majority's decision to uphold a state law allowing white-only primaries was fundamentally flawed and inconsistent with constitutional principles. He contended that by permitting such discriminatory practices, the Court was effectively endorsing racial segregation and undermining democratic values. Furthermore, he asserted that political parties should not be allowed to circumvent federal laws prohibiting racial discrimination simply because they are private entities; rather, they must adhere to these laws when conducting public functions like primary elections. In his view, this case represented an opportunity for the Supreme Court to affirm its commitment to equal rights and justice under law - an opportunity it had regrettably missed.