Southerners had blundered monumentally. They had assumed that what Andrew Johnson was willing to accept, Republicans would accept as well. But southern intransigence compelled even moderates to conclude that ex-rebels were a “generation of vipers,” still untrustworthy and dangerous. The black codes became a symbol of southern intentions to “restore all of slavery but its name.” “We tell the white men of Mississippi,” the Chicago Tribune roared, “that the men of the North will convert the State of Mississippi into a frog pond before they will allow such laws to disgrace one foot of the soil in which the bones of our soldiers sleep and over which the flag of freedom waves.”

The moderate majority of the Republican Party wanted only assurance that slavery and treason were dead. They did not champion black equality, the confiscation of plantations, or black voting, as did the Radical minority within the party. But southern obstinacy had succeeded in forging unity (at least temporarily) among Republican factions. In December 1865, Republicans refused to seat the southern representatives elected in the fall elections. Rather than accept Johnson’s claim that the “work of restoration” was done, Congress challenged his executive power.

Republican senator Lyman Trumbull declared that the president’s policy meant that an ex-slave would “be tyrannized over, abused, and virtually reenslaved without some legislation by the nation for his protection.” Early in 1866, the moderates produced two bills that strengthened the federal shield. The first, the Freedmen’s Bureau bill, prolonged the life of the agency established by the previous Congress. Arguing that the Constitution never contemplated a “system for the support of indigent persons,” President Andrew Johnson vetoed the bill. Congress failed by a narrow margin to override the president’s veto.

The moderates designed their second measure, what would become the Civil Rights Act of 1866, to nullify the black codes by affirming African Americans’ rights to “full and equal benefit of all laws and proceedings for the security of person and property as is enjoyed by white citizens.” The act boldly required the end of racial discrimination in state laws and represented an extraordinary expansion of black rights and federal authority. The president argued that the civil rights bill amounted to “unconstitutional invasion of states’ rights” and vetoed it. In essence, he denied that the federal government possessed the authority to protect the civil rights of African Americans.

In April 1866, an incensed Republican Party again pushed the civil rights bill through Congress and overrode the presidential veto. In July, it passed another Freedmen’s Bureau bill and overrode Johnson’s veto. For the first time in American history, Congress had overridden presidential vetoes of major legislation. As a worried South Carolinian observed, Johnson had succeeded in uniting the Republicans and probably touched off “a fight this fall such as has never been seen.”