Only three U.S. Presidents have been tried in the Senate on articles of impeachment. Nixon resigned prior to charges, leaving Johnson, Clinton, and Trump (twice) with the rare distinction. Andrew Johnson came the closest to removal as the required ⅔ majority failed by a single vote. Pairs with Constitutional violations such as treason, bribery, and other high crimes and misdemeanors, and ultimately partisan politicians not giving a shit. 

Suggested Listening: Impeach the President - the Honeydrippers