The 15th amendment was passed after Lincoln's assassination.
Passed by Congress February 26, 1869. Ratified February 3, 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 the power to enforce this article by appropriate legislation.