The Constitution permits Congress to remove presidents before their term is up if enough lawmakers vote to say that they committed “treason, bribery, or other high crimes and misdemeanors.”
Only three presidents have been subjected to impeachment proceedings. Two were impeached but acquitted and stayed in office: Andrew Johnson in 1868 and Bill Clinton in 1998 and 1999. A third, Richard M. Nixon in 1974, resigned to avoid being impeached.
What is the process?
First, the House of Representatives votes on one or more articles of impeachment. If at least one gets a majority vote, the president is impeached — which essentially means being indicted. (In both the Nixon and the Clinton cases, the House Judiciary Committee considered the matter first.)
Next, the proceedings move to the Senate, which holds a trial overseen by the chief justice of the Supreme Court.
A team of lawmakers from the House, known as managers, play the role of prosecutors. The president has defense lawyers, and the Senate serves as the jury.
If at least two-thirds of the senators find the president guilty, he is removed, and the vice president takes over as president. Note that two-thirds of the Senate — 67 votes — is a very high threshold that’s almost never achieved on any matter that’s remotely partisan. The framers did not make it easy for Congress to remove a democratically elected president from power.
What are the rules?
There are no standard rules. Rather, the Senate passes a resolution first laying out trial procedures.
“When the Senate decided what the rules were going to be for our trial, they really made them up as they went along,” said Greg Craig, who helped defend Mr. Clinton in his impeachment proceeding and later served as White House counsel to President Barack Obama.
What are the standards?
The Constitution allows for the impeachment and removal of a president for “treason, bribery, or other high crimes and misdemeanors.” But no controlling authority serves as a check on how lawmakers choose to interpret that standard, which makes it as much a question of political will as of legal analysis.