Since this is being talked about a lot right now, for obvious reasons, let's go over what the law actually provides for the removal of a sitting president.
Option A: Impeachment
Step A0: Not required, but the House may start an investigation. (This is what happened to Nixon.)
A1: A Resolution is introduced formally calling for impeachment. This is usually referred to the Judiciary Committee to debate, who may approve it, upon which the full House votes on it.
/2