UPDATE Cardinal Mueller , in his most recent Interview, has expressed a position very much like that adopted by Tom Weinandy. Here is the Lifesitenews text:
" As soon as [the bishops] teach and decide something contrary to the Apostolic doctrine and the sacramental constitution of the Church, they have lost the right to the 'religious obedience of the faithful' (Lumen Gentium 25; Dei Verbum 10). Already many bishops in the course of Church history have become heretical or led their parishes in schism, as for example the Donatists, who, with their majority, stood up to the Catholics in North Africa."
As a poor sad old product of the intellectual passions of the 1960s, I still ... Yes!! ... believe in the importance of the cause of Christian Unity. Every morning this week, I have offered that marvellous old Mass ad tollendum schisma, with those moving lections from S Paul ad Ephesios, and the Lord's High Priestly Prayer. It has profoundly affected me.
Of course, I have been aware that currently we should be praying, not least, for the Unity of all those who are already in Full Communion with the See of S Peter. And suddenly, there came into my mind (by chance, if you believe in chance) memories of the teaching of Fr Thomas Weinandy (lecture, February 2018, in Sidney).
Weinandy, once Warden of Greyfriars in this University and, until he was sacked, a Very Big Man on the theological Commission of the USA Episcopal Conference, analysed the ecclesiology of S Ignatius the Matyr.
In the course of this, he discussed the position of a bishop who "espouse[d] heretical teaching, whether concerning doctrine, morals, or pastoral and sacramental practice which bears upon doctrine and morals". He argued that "such a bishop no longer was in union with the catholic ecclesial community for he no longer professed the one apostolic faith of the Church and thus rendered himself incapable of exercising fully his office as bishop. ... He may continue to act outside the Church, or even within the Church, but his actions would would lack a genuine ecclesial character, for the essential and indispensible four marks of the Church would be absent within his specious ministry".
[I myself might have said: "was no longer in full union withe catholic ecclesial community".]
Fr Tom remarked:"I similarly employ [this argument] in the face of our contemporary ecclesial crisis". I agree. His judgement would apply, in my opinion, to any bishop who fitted his analysis, from the servus servorum Dei upwards.
I am sustained in this opinion by its closeness to the teaching of our Patron S John Henry Newman. Analysing ecclesiologically the Arian Crisis, he argued that, during that period, the Magisterium of the Ecclesia docens was in suspense: in the sense that, as an objective historical fact, bishops from the pope downwards were, whether because of their own heresy or because of fear and intimidation, not de facto exercising the sacred teaching ministry vested in them.
We must, I believe, pray that all those bishops, high and low, whose ministry is thus sadly and gravely vitiated may, with the help of God's grace, return to the exercise of an episcopal ministry which possesses "a genuine ecclesial character", thus coming fully back into the Unity for which Christ prayed, and restoring to the Church her Oneness, her Holiness, her Catholicity, and her Apostolicity.