He may try to argue he took them while he was president, and therefore, no charges can be filed. Actions and motives while the president can not be looked at either.
I am sure Jack Smith can argue all the other crimes of keeping, obstructing, and distributing the documents to those with out security clerence is still a crime but it’s if the question of his legitimacy if the reason. I think the SCTUS will agree with Cannon over the actual law for some BS reasons the founding fathers are believed to have said along time ago.