The White Court unanimously ruled in Guinn v. United States (1915) that an Oklahoma voting law violated the Fifteenth Amendment, which protects the right of suffrage. The Oklahoma law provided that no person could vote unless he could read and write any section of the Oklahoma Constitution. The law also provided, however, that this literacy provision did not apply to those who were eligible to vote before January 1, 1866, the date the Fifteenth Amendment was passed. This “grandfather” clause essentially meant that illiterate whites could vote but not blacks.

The White Court ruled that this provision “re-creates and perpetuates the very conditions which the Amendment was intended to destroy”—the right to vote based on race. The Court, in an opinion by Chief Justice White, deemed it repugnant to base eligibility to vote on a person’s status, or that of their ancestors, in 1866.