Philippe Duplessis-Mornay, A Defense of Liberty Against Tyrants Duplessis-Mornay mentions magistrates as well as kings. Who was the magistrate, and

Philippe Duplessis-Mornay, A Defense of Liberty Against Tyrants

Duplessis-Mornay mentions magistrates as well as kings. Who was the magistrate, and what was his role in relation to the king?  Under what circumstances should he challenge the king's authority? Why? In a similar position, how should a individual respond to the actions of a magistrate if he disapproves of his conduct? Why was this different?