If anyone who sits in Peter's chair were considered pope then the antipope Anacletus who lasted usurping the papacy for 8 years would be Saint Peter's successor

  We want Muller to answer us if a heretic can become Pope?

Bergoglio was disqualified from became a pope due to his heretical, apostate and schismatic past in Argentina.

 As I keep repeating, the heresiarch Jorge Mario Bergoglio is not a pope who has fallen into heresy, but being already a heretic in Argentina he was invalidly elected pope. 

The case of Pope Honorius I, who after his death was declared a heretic is a historical fact that refutes Muller's claim. "No canonical process can declare a Pope a heretic"

Honorius' successor St. Leo II approved. "We anathematize the inventors of the new error, that is, Theodore, Sergius, ... and also Honorius, who did not attempt to sanctify this Apostolic Church with the teaching of Apostolic tradition, but by profane treachery permitted its purity to be polluted."

In this case of Pope Honorius it is argued that this case does not prove that heretics can be popes, since the Church has never stated that he remained pope after his fall into heresy. 

St. Alphonsus Liguori (1787), Doctor of the Church: "If ever a pope, as a private person, should fall into heresy, he would at once fall from the Pontificate."

 In the Case of Antipope Anacletus II who usurped Peter's chair for 8 years because he had the support of the college of cardinals, it was Saint Bernard of Carvajal after the death of the antipope who put an end to the Schism caused by antipope Anacletus. Here we see a simple priest confronting an antipope, as Archbishop Carlo Maria Viganò can do with the authority he has. Let us pray that Saint Bernard of Carvajal helps us fight the false Pope Bergoglio.

Bergoglio's Homosexual Subversion Already Began in Buenos Aires

Father Felix Sarda said: “The apostate priest is the first factor the devil are looking for his work in this rebellion. He need to present it in a way authorized in the eyes of the unwary, and no use for it as much as the endorsement of a minister of the Church. And, unfortunately, she never missing corrupt clerics in their habits, the most common way of heresy; or blind arrogance, also very common cause of all error...”

“Contra factum non valet argumentum”

Bergoglio usurps the papacy. These are two very different things and the Magisterium of the Church makes the elevation of a heretic as pope invalid and void. The antipope  Anacletus lasted 8 years usurping the papacy and Bergoglio has been there for 10 years.

“Those capable of being validly elected are all who are not prohibited by divine law or by an invalidating ecclesiastical law… Those who are barred as incapable of being validly elected are all women, children who have not reached the age of reason; also, those afflicted with habitual insanity, the unbaptized, heretics, schismatics…” (Wernz-Vidal, Jus Canonicum 1:415)

Catholic Encyclopedia 1914 (Vol. 11, p. 456):

“It is very clear that the election [as Pope] of a heretic, schismatic or woman would be null and void.”

“Cum ex Apostolatus Officio” – Apostolic Constitution of Pope Paul IV About the Danger of Heretical Authorities

6. In addition, [by this Our Constitution, which is to remain valid in perpetuity We enact, determine, decree and define:] that if ever at any time it shall appear that any Bishop, even if he be acting as an Archbishop, Patriarch or Primate; or any Cardinal of the aforesaid Roman Church, or, as has already been mentioned, any legate, or even the Roman Pontiff, prior to his promotion or his elevation as Cardinal or Roman Pontiff, has deviated from the Catholic Faith or fallen into some heresy:

(i) the promotion or elevation, even if it shall have been uncontested and by the unanimous assent of all the Cardinals, shall be null, void and worthless;

(ii) it shall not be possible for it to acquire validity (nor for it to be said that it has thus acquired validity) through the acceptance of the office, of consecration, of subsequent authority, nor through possession of administration, nor through the putative enthronement of a Roman Pontiff, or Veneration, or obedience accorded to such by all, nor through the lapse of any period of time in the foregoing situation;

(iii) it shall not be held as partially legitimate in any way;

(iv) to any so promoted to be Bishops, or Archbishops, or Patriarchs, or Primates or elevated as Cardinals, or as Roman Pontiff, no authority shall have been granted, nor shall it be considered to have been so granted either in the spiritual or the temporal domain;

(v) each and all of their words, deeds, actions and enactments, howsoever made, and anything whatsoever to which these may give rise, shall be without force and shall grant no stability whatsoever nor any right to anyone;
(vi) those thus promoted or elevated shall be deprived automatically, and without need for any further declaration, of all dignity, position, honour, title, authority, office and power.

7. Finally, [by this Our Constitution, which is to remain valid in perpetuity, We] also [enact, determine, define and decree]: that any and all persons who would have been subject to those thus promoted or elevated if they had not previously deviated from the Faith, become heretics, incurred schism or provoked or committed any or all of these, be they members of anysoever of the following categories: the Cardinals, even those who shall have taken part in the election of this very Pontiff previously deviating from the Faith or heretical or schismatical, or shall otherwise have consented and vouchsafed obedience to him and shall have venerated him;

Castellans, Prefects, Captains and Officials, even of Our Beloved City and of the entire Ecclesiastical State, even if they shall be obliged and beholden to those thus promoted or elevated by homage, oath or security; shall be permitted at any time to withdraw with impunity from obedience and devotion to those thus promoted or elevated and to avoid them as warlocks, heathens, publicans, and heresiarchs (the same subject persons, nevertheless, remaining bound by the duty of fidelity and obedience to any future Bishops, Archbishops, Patriarchs, Primates, Cardinals and Roman Pontiff canonically entering).
To the greater confusion, moreover, of those thus promoted or elevated, if these shall have wished to prolong their government and authority, they shall be permitted to request the assistance of the secular arm against these same individuals thus promoted or elevated; nor shall those who withdraw on this account, in the aforementioned circumstances, from fidelity and obedience to those thus promoted and elevated, be subject, as are those who tear the tunic of the Lord, to the retribution of any censures or penalties.

8. [The provisions of this Our Constitution, which is to remain valid in perpetuity are to take effect] notwithstanding any Constitutions, Apostolic Ordinations, privileges, indults or Apostolic Letters, whether they be to these same Bishops, Archbishops, Patriarchs, Primates and Cardinals or to any others, and whatsoever may be their import and form, and with whatsoever sub-clauses or decrees they may have been granted, even “motu proprio” and by certain knowledge, from the fulness of the Apostolic power or even consistorially or otherwise howsoever; and even if they have been repeatedly approved and renewed,have been included in the corpus of the Law or strengthened by any capital conclaves whatsoever (even by oath) or by Apostolic confirmation or by anysoever other endorsements or if they were legislated by ourself. By this present document instead of by express mention, We specially and expressly derogate the provisions of all these by appropriate deletion and word-for-word substitution, so that these may otherwise remain in force.