Alcorn resigned the governorship to become a U.S. senator (1871 to 1877), replacing his ally Hiram Revels, the first African-American U.S. senator from the state. In speeches to the Senate, Alcorn urged the removal of the political disabilities of white southerners and rejected Radical Republican proposals to enforce social equality by federal legislation. He denounced the federal cotton tax as robbery, and defended separate schools for both races in Mississippi. Although a former slaveholder, he characterized slavery as "a cancer upon the body of the Nation" and expressed his gratitude for its end.