Pope Nicholas I to Catholic bishops in Lorraine:
“You affirm that you are submissive to your sovereign, in order to obey the words of the apostle Peter, who said, ‘Be subject to the prince, because he is above all mortals in this world.’ But you appear to forget that we, as the vicar of Christ, have the right to judge all men: thus, before obeying kings, you owe obedience to us; and if we declare a monarch guilty, you should reject him from your communion until we pardon him.
“We alone have the power to bind and to loose, to absolve Nero and to condemn him; and Christians can not, under penalty of excommunication, execute other judgment than ours, which alone is infallible. People are not the judges of their princes; they should obey without murmuring the most iniquitous orders; they should bow their foreheads under the chastisements which it pleases kings to inflict on them, for a sovereign can violate the fundamental laws of the State, and seize upon the wealth of the citizen, by imposts or by confiscations; he can even dispose of their lives, without any of his subjects having the right to address to him simple remonstrances. But if we declare a king heretical and sacrilegious, if we drive him from the Church, clergy and laity, whatever their rank, are freed from their oaths of fidelity, and may revolt against his power.”
(Source: A Complete History of the Popes of Rome, from Saint Peter, the First Bishop to Pius the Ninth, the Present Pope: Including the History of Saints Martyrs, Fathers of the Church, Religious Orders, Cardinals, Inquisitions, Schisms and the Great Reformers (Google eBook), by Louis Marie DeCormenin, James L. Gihon, 1857, p. 242.)