Thus far, nearly two-and-a-half centuries into the nation's history, only three presidents have been faced impeachment proceedings. The first, as described in the introduction, was Andrew Johnson, the second was Richard Nixon and the third was Bill Clinton.
In the case of Andrew Johnson, Congress passed a piece of legislation called the "Tenure of Office Act," which was designed to stop the president from firing a cabinet member without Congress's approval. It's pretty clear they were hoping he would break this law and it should be noted that the act was later struck down as unconstitutional. But while it lasted, it served its purpose because Johnson duly fired his Secretary of War and the House quickly issued Articles of Impeachment. As we said earlier, the effort to get rid of Johnson was doomed to fail by just one vote.
Richard Nixon's presidential career began to nose-dive after it was discovered that he and his administration used a variety of dirty tricks and illegal methods to sabotage the Democratic party, most notably breaking into the Watergate hotel. When he lost the support of his own party, it became clear that he would likely be impeached and almost certainly removed from office. But Nixon deprived Congress of that satisfaction and, in a "you're-fired-I-quit" scenario, he resigned.
Bill Clinton was infamously caught perjuring himself when he lied to a grand jury about his relationship with a White House intern named Monica Lewinsky. On the strength of that perjury, the Republican-dominated House of Representatives voted to impeach him. The proceedings then moved to the Republican-led Senate. Because the constitutional wording for trials of impeachment in Article 1, Section 3 are so brief, there are no set rules as to how the Senate trial must proceed. Essentially, the senators made it up as they went along.
For instance, during Bill Clinton's impeachment, the Senate decided to give the "managers" only four days to present their case and the president's defense team four days to defend him. As for witnesses, it wasn't even clear if any would be permitted to testify at all. Eventually a few gave videotaped depositions [source: Savage].
The fact that the Senate, which essentially serves as the jury in these proceedings, can determine the rules of the trial, underlines how unique a process impeachment is. It's hard to imagine a jury in a criminal case dictating how long an opening statement can be. In any case, the impeachment process foundered when the Senate acquitted Clinton with a 50-50 vote, far short of the two-thirds required to convict [source: Savage].