The first President of the United States to be impeached was Andrew Johnson in 1868. Johnson, who succeeded Abraham Lincoln, faced impeachment primarily due to his violation of the Tenure of Office Act by attempting to remove Edwin M. Stanton, the Secretary of War, without Senate approval. This act was seen as a challenge to Congressional authority during the Reconstruction era. The House of Representatives impeached Johnson, but he was acquitted by the Senate, falling just one vote short of the required two-thirds majority for removal. This event set vital precedents regarding presidential powers and the impeachment process.