The Framers intended for removal from office to be the final step in a two-part process. The process begins in the House of Representatives. Articles of impeachment approved by the House are similar to a criminal indictment by a grand jury: they are a list of unproven accusations.
The Constitution gives the sole Power of Impeachment to the House. The House can approve articles of impeachment by a simple majority. As a practical matter, the category of “High Crimes and Misdemeanors” includes whatever the House says it does.
With that said, America’s founders took this phrase from English common law, where it had developed a definition. It is a narrow category of serious misconduct requiring removing the president now, rather than waiting for the next election.
If the House issues charges, the process ends in a trial-like hearing before the U.S. Senate. Thus, two goals would be achieved. There will be a full public inquiry into allegations. Then, if necessary, the adjudication of those charges is done in the Senate. Conviction in the Senate requires a two-thirds majority for removal from office.
The Senate has the “Sole Power to try all Impeachments.” The Constitution does not explicitly require the Senate to act on the articles of impeachment. It also does not require it to hold a trial. However, if the Senate opts for a trial, under congressional rules, members the House serve as impeachment “managers” and have the role of prosecutors.
The Chief Justice of the Supreme Court presides at the impeachment trial of a president. A presidential impeachment trial occurs before the entire Senate. In these trials, Senators have a role that combines features of both judge and jury. Senators have the authority to govern the conduct of the trial and decide any evidentiary issues that may arise. Impeachment trials of other officials, under rules established by the Senate, take place before an impeachment trial committee of senators. This is the impeachment process… what happens.