The U.S. Senate has held only eighteen impeachment trials in two hundred and thirty years, and only twice for a President. Because impeachment happens so infrequently, it’s hard to draw conclusions about what it does, or even how it works, and, on each occasion, people spend a lot of time fighting over the meaning of the words and the nature of the crimes. Every impeachment is a political experiment.
Jill Lepore, “You’re Fired”, The New Yorker (28 October 2019), 28.