No president has ever been charged with crimes after he left office. Andrew Johnson was almost convicted while he was in office (the way impeachments work here is the House of Representatives, our lower house, votes on impeachment, then there's a criminal trial held in the Senate, our upper house). Richard Nixon was impeached over Watergate, resigned before he could be convicted, and the next president, Gerald Ford, pardoned him for everything he did or might have done almost immediately.