crimes or doing something unconstitutional.
The second President to be impeached was William J. Clinton, in 1998.
Nixon resigned as president due to Watergate while facing the threat of impeachment. He was not actually impeached.
If the President dies or if he resigns. Also If he is impeached.
The president must be formally charged with a crime (impeached) by the House of Reps. and then must stand trial in the US Senate. If convicted, he/she is removed. Impeached does not mean removed. We have impeached two presidents, but have never removed one.
None.