An impeachment is a lengthy process but how does it work? Impeachment requires a simple majority from the House Judiciary Committee, the House of Representatives and a two-thirds majority of the Senate. While each step is quite explicitly described by the constitution, the possible indictments are worded rather vaguely. Consequently, most attempts to impeach the president are rejected by the House Judiciary Committee.
There were only two cases in which it went all the way to the senate vote. But the cases of Andrew Johnson in 1868 and Bill Clinton in 1998-99 both fell short of the two-thirds majority of the Senators. The only actual withdrawal from office came from President Richard Nixon in 1974 after he deflected a potential impeachment by resigning. In his case, the loss of trust from his own party essentially left him with no other choice.