The below is from the Father Hardon Archives on new advent website. The Arian Heresy was HUGE. And the Great Apostasy (preceding the Return of Jesus Christ) predicted by Christ and St. Paul is said to be going to be the worst crisis ever, with a vast falling away from the faith and a deception so great as to possibly even deceive the elect. The Church isn’t going to remain Big forever therefore. As for heretical bishops in the Church, St. Paul predicted THEM, too, when he warned the Ephesian presbyters that “from among you yourselves” shall arise heretics seeking to lead the faithful away from the truth. We are under no obligation before God to obey a heretical bishop, even if he is our own bishop, for a heretic by divine law ceases to be a member of the church and by that fact falls ipso facto, without need for a church declaration, from his office and jurisdiction. Now, if God forbid the Great Apostasy is descending on us, we should not be shocked to find a growing number of heretical bishops. I believe that that Great Apostasy IS happening right now, yet Christ is still faithful to his promise to be with us “even to the end of the World.” Anyway, the brief article about Arianism below:
Spread of Arianism. Arianism had the advantage of clarity of position from the beginning. Its founder bequesthed his followers four principles from which they never wavered, even when their expression of doctrine was veiled under sematics.
God is absolute one, not only in nature but in person. He is in no sense generated. It is therefore impossible for Him to communicate His substance. He can only create things outside Himself out of nothing.
The Word or Logos is an intermediary between God and the world, existing before cosmic time but not eternal. Consequently there was a period when the Logos was not.
This means that the Logos was created. He was produced…
As a result, the nature of the Logos is to be fallible and peccable; He could both err and sin.
From these premises, Arianism developed a number of species…
Heading the list of Arian derivatives was Eusebianism, named after Eusebius of Nicomedia, friend and confidant of Arius… Eusebius should be held mainly responsible for the rise and spread of Arianism…
Pure Arians came to be called Anomoeans (anomoios = dissimilar). Founded by Aetius and Eunomeius, they are also known as Eunomians. They insisted that in God there is no internal generation, and therefore the Son of God is not consubstantial with the Father. Basil the Great and Gregory of Nyssa wrote extensively against them.
Semi-Arians, so called because they tried to straddle Nicea and Arius, are known to history in at least four species. The Homoeans (homoios - similar), also known as Acacians from their leaders, Acadius of Caesarea, claimed that the Logos is not numerically identical with the Father but like to it. Homoiousians (homoiousion = of like substance) were in the same class as the Homoeans but more philosophical…
The Macedonians are in a class by themselves. Their leader, Macedonius, usurped the See of Constantinople on two occasions, between 342 and 360 A.D., and his followers are best known for denying the divinity of the Second and Third Persons of the Trinity, with stress on the Holy Spirit.
Things quieted down while the Catholic Emperor Constans was in power but on his death in 350 A. D., the Arian Constantius became sole emperor.
Immediately there was an outcropping of Arian-sponsored councils…, where the anti-Nicene party triumphed through pressure (including physical violence) from imperial authority dominated by Arian bishops from the East. At the last two synods, most of the Catholic bishops were induced by fraud and forced to sign a noncommittal symbol of faith, which was then flaunted to the world as an Arian victory. St. Jerome commented on this period, that “The whole world sighed as it awoke in wonder to find itself Arian.” Actually the Christian world was not Arian; but many of its leaders had been betrayed into leaving that impression.
A sad illustration of the crisis through which the Church was passing is what happened to Pope Liberius (352-366 A. D.), the first pontiff to whom the title of “Saint” is not applied, probably because of his lack of courage under trial. He was seized at Rome by the Arian Emperor Constantius for his ardent defense of Athanasius and the Nicene Creed. After years of exile, and under threat of death, Liberius is reported to have signed a compromise formula as the price of restoration to the Roman See. When Constantius died (361 A4.), Liberius publicly condemned Arianism.