A formal accusation of wrongdoing against a public official. According to the United States Constitution, the House of Representatives can vote to impeach an official, but the Senate actually tries the case. Several presidencies have been blemished by impeachment or the threat of impeachment: President Andrew Johnson was impeached after the Civil War but was acquitted. President Richard Nixon resigned from office as the House of Representatives prepared to initiate impeachment proceedings. President William Jefferson Clinton was impeached in 1998 but was acquitted by the Senate the following year.