He has called Pope Francis a liberal “servant of Satan” and once suggested the Vatican’s Swiss Guards arrest the 87-year-old pontiff. Now, after receiving years of withering verbal attacks, Francis appears to have struck back against Archbishop Carlo Maria Viganò, the former Vatican ambassador to the United States and the pope’s most ardent internal critic.

The Vatican’s disciplinary body, the Dicastery of the Doctrine of the Faith (DDF), issued a formal decree, made public by Viganò on Thursday, assigning the senior cleric to a penal canon trial. The charges: the “crime of schism” and “denial of the legitimacy of Pope Francis.”

Such trials are exceedingly rare, and the move underscores a recent effort by the Vatican to take more formal action against a gaggle of archconservatives who have sought to undermine Francis’s papacy from the inside. Conviction could lead to Viganò’s defrocking and excommunication, ending the long career of the 83-year-old Italian cleric who has emerged as the leading symbol of a traditionalist resistance to a papacy perceived by him as wildly liberal.

The DDF is led by Argentine Cardinal Victor Manuel “Tucho” Fernández who recently created a firestorm with his Fidducia Supplicans and subsequent defense.

Viganò, a diminutive firebrand who delivers stinging missives on X and the conservative U.S. outlet LifeSiteNews, said in a statement that he saw the “accusations against me as an honor.” In his comments, Viganò — who has vowed to create a seminary free of Vatican interference — referred to Francis as he always does, eschewing his official title and using his name before he was pope: Jorge Mario Bergoglio.

“It is no coincidence that the accusation against me concerns the questioning of the legitimacy of Jorge Mario Bergoglio and … the ideological, theological, moral, and liturgical cancer of which the Bergoglian “synodal church” is the necessary metastasis,” Viganò wrote.