The following is a good video on the pope and heresy. However, please keep in mind that the video heavily emphasizes the hypothetical scenario of a true pope falling in public manifest formal heresy. Ecclesia Militans holds to the position that a true pope cannot become a public manifest formal heretic which is Opinion No. 1 of the Five Opinions expounded upon by St. Robert Bellarmine who himself held to this position. Fr. Paul Kramer holds that to deny Opinion No. 1 is proximate to heresy.