A presidential pardon can be granted at any time after commission of the offense: the pardoned person need not have been convicted or even formally charged with a crime.
Well, okay. My main question was whether the President could kill this move to criminalize political activity by using the pardon to neutralize the endless investigations case by case. Charge: pardon. Charge: pardon. Charge: pardon. Charge: pardon. Repeat until the cows come home.