As far as I’m concerned “after they leave office” should not even be a thing. If a president commits crimes while in office. There’s no reason they shouldn’t be prosecuted whenever there is enough evidence to prosecute them.
“Where, say some, is the King of America? In America the law is king. For as in absolute governments the King is law, so in free countries the law ought to be king; and there ought to be no other.” ~ Thomas Paine
Still better than what Republicans are offering