All of them? It's been shown to be common practice, Faun! In Trump's instance however it was deemed to be worthy of a raid on his home by the FBI! Bill Clinton kept classified documents in his sock drawer yet he wasn't bothered at all. Joe Biden kept them and he wasn't even the President...just the Vice President and he's allowed to do a Sgt. Schultz rountine? "I know nothing!"?What other president kept classified documents after leaving office?