As the only southern senator to support the Union in the American Civil War he was appointed military governor of Tennessee. Having been elected as Vice-President to Abraham Lincoln in 1864, he became President as a result of Lincoln’s assassination in April 1865. His reconstruction policy, which failed to protect the interests of former slaves in the ex-Confederate states, brought him into bitter conflict with the Republican majority in Congress: his vetoes of several reconstruction measures were overridden by two-thirds majorities in Congress. His dismissal of his Secretary of War, Edwin Stanton (in defiance of a Tenure of Office Act) led to his impeachment (a US legal procedure for removing officers of state before their term of office expires), and Johnson only survived by a single vote in the Senate (1868). He returned to the Senate in 1875 but died soon after.