Well, no, an impeachment conviction just asks 'Should this man be president?' So senility is not a defense.
But if he isn't of sound mind, then isn't it up to the Cabinet or some other body to remove him? Isn't there some method other than a conviction for incompetent people?
Yes, but both the 25th and the impeachment process assume that only one person in the equation lacks ethics, honor, attention span, soul.
Well, no, an impeachment conviction just asks 'Should this man be president?'
What other recourse is there for crimes in office? Can something happen post impeachment?
Sure.
The DOJ just has a
policy of not indicting a sitting president. Nothing in any law prevents taking his ass to court.
Once he's out of office, either by not being reelected or by being impeached, or resigning, or being booted out through the 25th Amendment, he's subject to all prosecution.
Unless the next pres pardons him.
All impeachment would have done with Nixon is get him out of office and end his benefits of retirement. No secret service, no pay, no stipend for the Nixon Library, and so on. The impeachment would not have sent him to jail.
But without Ford's pardon, the FBI would have prosecuted him for everything they could prove. Such as knowledge of or direction to perform the things everyone else was going to jail for.
If Trump tries a senility defense at the impeachment, starts babbling like a loon, or showing up with Barron as his legal counsel, shits his pants on the Senate floor, making finger -guns and shooting his accusers, he's going to force the Senate to convict, which will just make him not-be-President. Free and clear unless the FBI is waiting in the hallway with a pair of handcuffs for the INSTANT the vote is completed.