Fifteenth amendment to the u. s. constitution (1870) section 1. the right of citizens of the united states to vote shall not be denied or abridged by the united states or by any state on account of race, color, or previous condition of servitude. section 2. the congress shall have power to enforce this article by appropriate legislation. which of the terms listed here proved to be the greatest obstacle to the fifteenth amendment? a) poll taxes b) closed primaries c) 19th amendment d) dred scott v. sandford