This is my opinion, but it is not a matter of faith. Of course, Bellarmine's counsel about the theoretical possibility of a manifestly heretical Pontiff ought to be held together with his comments elsewhere:
Moreover, even though somewhere, by God's permission, a credulous people should be easily seduced by their pastor, no Catholic would dare say that therefore the people should be discouraged from obeying their prelates, or should themselves become judges of their pastors, and decide on the doctrine that is being preached to them. We know from present experience among the Lutherans that the danger of heresy is far greater by making this kind of concession to human liberty, than it will ever be from the simple obedience of the people. ("Tractatus de obedientia," in Auctarium Bellarminianum, ed. Le Bachelet (Paris, 1913), p. 385)
Thanks for posting that. I'm just curious as to at what point God has suspended the free will of the Pontiff in order to prevent him from being in error.
As far as the second quote you gave from Bellarmine. That is a very temporal statement he refers to with his reference to Lutherans.
Today's circumstances are quite different from then.
By God's permission the majority of bishops and prelates can credulously be seduced by their pastors and then pass it along to the credulous masses.