A two-thirds vote of the senators present is required to convict the president after an impeachment inquiry. Punishment is limited to removal from office, although the accused can still be subject to criminal proceedings in the courts after impeachment. In medieval times, the English parliament developed the process as a means to exercise some measure of control over the King. They modified the practice to discourage the misuse of impeachment as a tool of political advantage. However, the attempt to impeach President Andrew Johnson in 1868 clearly breached this intent and many would argue that the 1998 attempt to impeach President Clinton is similarly politically motivated.
Impeachment occurs frequently at the state level of American politics.
Since the adoption of the federal Constitution, all states except Oregon have adopted the practice of impeachment. No US president has ever been dismissed after an impeachment inquiry, although Johnson and Richard Nixon came close. In 1868, in the tumultuous years after the American Civil War, the northern-dominated Congress voted to impeach Johnson, who came from the South. Johnson survived the Senate trial by a single vote. In the 1974 Watergate scandal, the House of Representatives judiciary committee approved articles of impeachment against Nixon, but he resigned before he could be formally thrown out.