“Although the Counter-Reformation canonists were understandably phobic about the impetus such a doctrine as that of automatic loss of the papal office for heresy without the judgment of the Church might give occasion to the abusive application of the Protestant principle of Private Judgment against the Papacy, the ancient age-old principle of law (Ab abusu ad usum non valet consequentia) remains ever valid, that an abuse is no argument against legitimate use; and therefore, Abusus non tollit usum: the abuse of a right does not nullify the right to its legitimate exercise. Their understandable concern for the possibility and even the likelihood that private individuals could seize upon the right to judge privately as a matter of conscience, and abuse it in the manner that it was abused by Luther to pronounce the pope a heretic, led them to adopt the opposite extreme, equally harmful and heterodox, according to which even a manifestly heretical pope remains in office and retains jurisdiction until the Church, by a juridical act pronounces judgment on him; and that private individuals may not avail themselves of their God-given right and last means of defense against the ravenous wolf, to form an opinion to acknowledge the defection and loss of office resulting from even the most manifest and patent public rejection of the Catholic faith by a heretic pope; and as a consequence to be compelled to remain subject to him, and be in communion with the public enemy of the Church for months, years or even decades, until the Church, by some miracle of providence, can finally be able to pronounce a judgment which effectively results in the heretic’s removal.”
Kramer, Paul. To Deceive the Elect: The Catholic Doctrine on the Question of a Heretical Pope (Kindle Locations 11153-11165). Kindle Edition.
Note: Fr. Paul Kramer holds that a true pope cannot be a formal heretic. In his estimation, this is proximate to Faith. The point of the quote above is to emphasize that one can privately legitimately judge a cleric as a formal heretic upon the fact of public manifest formal heresy.