Having previously served as a senator and later military governor for the state of Tennessee, Andrew Johnson was chosen by Abraham Lincoln to be his running mate in the election of 1864. Having been the only senator from a seceding state to remain loyal to the Union at the outbreak of the Civil War, he secured the support of “Union Democrats” and consequently became Vice President.
Johnson’s inauguration took place on 4 March 1865, but exactly six weeks later he became President of the United States after Lincoln was assassinated by John Wilkes Booth. This coincided with the end of the Civil War, leaving him to introduce a lenient Reconstruction policy towards the defeated South that was vehemently opposed by the Radical Republicans in Congress. They passed laws to protect the rights of freed slaves, but the President vetoed them. In response Congress passed the Tenure of Office Act that stopped the President removing opponents from the cabinet by stating that the Senate had to approve the dismissal of officials.
Johnson defied the act in 1867 when he sought to replace the Republican Secretary of War, Edwin M. Stanton, with General Ulysses S. Grant. The change was not approved and Stanton returned to the post after Grant resigned. On 21 February 1868 Johnson again dismissed Stanton and this time appointed General Lorenzo Thomas in his place, but Stanton refused to go and locked himself inside his office.
Although effectively a test of the constitutionality of the Tenure of Office Act, Johnson’s actions saw him impeached on 24 February. He was acquitted on 16 May by just one vote.