“Heretics and schismatics are barred from the Supreme Pontificate by the divine law itself… [T]hey must certainly be regarded as excluded from occupying the throne of the Apostolic See, which is the infallible teacher of the truth of the faith and the center of ecclesiastical unity.”
(Maroto, Institutiones I.C. 2:784)
“Appointment to the Office of the Primacy. 1. What is required by divine law for this appointment… Also required for validity is that the one elected be a member of the Church; hence, heretics and apostates (at least public ones) are excluded.”
(Coronata, Institutiones I.C. 1:312)
“All those who are not impeded by divine law or by an invalidating ecclesiastical law are validly eligible [to be elected pope]. Wherefore, a male who enjoys use of reason sufficient to accept election and exercise jurisdiction, and who is a true member of the Church can be validly elected, even though he be only a layman. Excluded as incapable of valid election, however, are all women, children who have not yet arrived at the age of discretion, those afflicted with habitual insanity, heretics and schismatics.”
(Wernz-Vidal, Jus Can. 2:415)
Source: http://www.fathercekada.com/2007/06/25/can-an-excommunicated-cardinal-be-elected-pope/
Note: Ecclesia Militans accepts all popes from John XXIII to Benedict XVI as true popes because the indicia of heresy do not amount to public manifest formal heresy in their cases. For more on this, please refer to Fr. Paul Kramer’s two volume set of To Deceive the Elect.
St. Athanasius the Great, Bishop of Alexandria, Confessor and Doctor of the Church, “Father of Orthodoxy” † (296-373) wrote to his flock during the dark days of the Arian Heresy.
EXCERPTED as follows:
For they hold the places, but you the Apostolic Faith. They are, it is true, in the places, but outside of the true Faith; while you are outside the places indeed, but the Faith, within you. Let us consider whether is the greater, the place or the Faith. Clearly the true Faith. Who then has lost more, or who possesses more? He who holds the place, or he who holds the Faith? Good indeed is the place, when the Apostolic Faith is preached there, holy is it if the Holy One dwell there. But ye are blessed, who by faith are in the Church, dwell upon the foundations of the faith, and have full satisfaction, even the highest degree of faith which remains among you unshaken. For it has come down to you from Apostolic tradition. . .