Perhaps I didn't make myself clear. It is legitimate to dismiss Salza and Siscoe's arguments precisely because there is another explanation for why these men are not popes. The fact that they are not popes is proven by their promulgation of evil and false morals and doctrines. The reason they are not popes need not be a fall from the papacy entailing complicated legal justification. By showing that the sin of heresy renders a man incapable of valid election, Father neatly sidesteps any need to engage all the legalistic arguments championed by Salza & Siscoe, and now taken up by the semivacantists at MHT.
It would be good to have examples of manifest heresy prior to their elections, but it's not necessary. It is simply one likely way to explain why they did not enjoy the protection of the Holy Ghost afforded to a true pope. Their non-papacy is proven by their actions as claimants to the throne.
Please don't misquote me. I said it was "reasonable to asssume" they were heretics prior to election since they can easily be shown to have been such after election. This is silly to deny. Is it more reasonable to conjecture that they suddenly abandoned their strict orthodoxy after being "elected?" Neither did I assert that they "lost membership in the Church based on 'assumptions.'" I said that since we know them to be heretics it is reasonable to assume they were also such prior to election, and that a LIKELY explanation for their lack of authority could be their having comitted a public sin of heresy. After all for a sin to have been public in the sense described by theologians it is by no means necessary that we be able to find a quote on google. It is a likely scenario.
Again I am not saying this is sufficient to prove their non-papacy, but rather that it is a reasonable possibility as to how and why they failed to become popes.
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Yes, I think his point is that it's obvious that they were heretics after their election, so they must have been heretics before their election.
I think Fr. Cekada's argument is that the five opinions of St. Robert Bellarmine, for example, that Sisco and Salza are always going on about, are actually a red herring inasmuch as they assume these guys were valid popes to begin with. St. Robert Bellarmine is talking about someone who is unquestionably pope, who is publicly Catholic, but who later (ad arguendo) publicly falls from the faith. That is not the case here, as the modernist anti-popes were modernist from the very beginning of their anti-reign, so it only makes sense to assume they were heretics before their election.
And a heretic cannot validly be elected pope. This makes the John of St. Thomas and Cajetan moot.
This is a reductio ad absurdum argument, as Fr. Cekada made it. He said either these people were faithful Catholics before their election and somehow turned into raging heretics as soon as they were elected

, or they were heretics already and the election was invalid.
Since the first possibility is

, the second one must be true.