In a discussion about the current election and the possibility of an indictment being handed down after a candidate was nominated, the possibility was raised that the President may have already issued a pardon, classified it as secret, and informed the DoJ of the pardon and its classified status. And that may be the reason that the DoJ has not, and will not seek an indictment.
Is there anything that would prevent this sort of political maneuver explicitly? Is there any precedence that would allow/disallow this sort of action?
NOTE: I am not asking if this has happened or for any speculation on what might happen if it were to come out.