And this goes to show that +Bellarmine is wrong on this point, as his arguments are based on Luke 22 and a history of no heretical popes. In his time, his arguments make sense.
Fast forward to today, and adding in V1 and V2, and his opinion is completely unfounded.
1. Luke 22, which is a general statement, and unexplained by Christ, was explained by V1.
2. V2 and the popes of this era have shown it possible that a pope is a heretic.