I've remarked elsewhere that this is an option and in fine Trump style. Outfox them at the last hour by resigning, making Pence the shortest-term president ever, making impeachment moot, and leaving Pence with the nasty work of attending the inauguration of the faux potus. Then a well-deserved vacation and plans for 2024.
Can’t they still impeach after a President has resigned?
Seems I recall that being bandied about, with 0blama.
That will not stop Impeachment, they can continue whether he is in office or not and they will.