The first president to be impeached in the United States was Andrew Johnson in 1868. Johnson, who became president after Abraham Lincoln's assassination, faced significant opposition from Congress due to his Reconstruction policies and conflicts over the Tenure of Office Act. His impeachment arose from his attempts to remove Edwin Stanton, the Secretary of War, from office without congressional approval. The House of Representatives voted to impeach Johnson, but he was acquitted by the Senate, falling just one vote short of the two-thirds necessary for removal. His impeachment marked a critical moment in the balance of power between the presidency and Congress.