Impeachment is a process of accusing an official in unlawful activity. The outcomes of impeachment are various for different countries. An official may be removed from office or even be punished as a criminal. In today's world such a measure as impeachment is often considered obsolete for modern politics and is used quite rarely. Anyway, it is still possible in most of the countries.

In the USA, the president may be convicted by the Senate after his impeachment. If this occurs, the President is removed from office and is replaced by the Vice President. A convicted president can also be prohibited from holding any public office in future. The verdict is always final and the former president can not appeal. By date, there have been no such cases in the US.

Note from history: Andrew Johnson and Bill Clinton have faced impeachment proceedings by the House of Representatives, but both of them were later acquitted. In Richard Nixon's case the impeachment was unsuccessful, as the president resigned before the vote.

Well, the right answer here is zero.

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