Congressman: "Could you charge the President with a crime after he left office?"
Mueller: "Yes."
This happened years ago in France in 2002 when Jean-Marie Le Pen ran against Jacques Chirac who if he lost the election stood liable to be arrested for corruption. as in the USA a French President in office cannot be arrested.
He ran the election on a platform of "What do you want a Crook or a Fascist" and won by a landslide and by the end of his second term had quashed all his indictable offenses.
Trumps seems to be fear mongering his way to "What do you want a Crook or a socialist" as his platform for 2020.