How does impeachment actually work?

Impeachment is a two-chamber process and the words get used imprecisely. The House of Representatives brings charges, called articles of impeachment, and adopts them by simple majority. That is impeachment, and it is analogous to an indictment rather than a conviction: the official remains in office. The Senate then holds a trial, with the Chief Justice presiding when a president is the defendant, and conviction requires a two-thirds vote. Conviction removes the official from office, and the Senate may hold a separate simple-majority vote to bar them from future federal office.

The constitutional standard is treason, bribery, or other high crimes and misdemeanors, a phrase inherited from English parliamentary practice that has never been definitively defined and does not require an indictable criminal offense, which is a source of perpetual argument. Impeachment applies to federal civil officers generally, not only presidents, and most actual removals in American history have been federal judges. Three presidents have been impeached, Andrew Johnson, Bill Clinton, and Donald Trump, who was impeached twice, and none was convicted by the Senate. Richard Nixon resigned before a House vote. Impeachment is also entirely separate from criminal prosecution, and the Constitution states explicitly that a convicted official remains liable to ordinary criminal proceedings.