“No one who is unwanted should be made a bishop; the desire and consent of the clergy and the people and the order is required.” —Saint Celestine I (pope 422-432)In the time before the legalisation of Christianity [Edict of Milan, 313], bishops were elected by all adult Christians in the parochia [the term 'diocese' was an imperial replacement]. St. Cyprian 258†, bishop of Carthage, wrote, quoting Paul to Timothy “that a bishop must not be 'litigious, nor contentious, but gentle and teachable.' ”* Cyprian also wrote, the people should not yield “their consent to the unjust and unlawful episcopacy of their overseer... since they themselves have the power either of choosing worthy priests and of rejecting unworthy ones.”**
“The one who is to be head over all should be elected by all.”— Saint Leo the Great (pope 440-461)
“It is essential to exclude all those unwanted and unasked for, if the people are not to be crossed and end by despising or hating their bishop. If they cannot have the candidate they desire, the people may all turn away from religion unduly.” —Leo the Great
There were bishops that were unanimously elected: the beautiful story of Fabian (a, b, c) coming to Rome  just as they were debating who should be the new pope, and when a dove perched on his head, he was chosen by that assembly of all believers as pope; Ambrose was a governor of Milan , he was a layman whilst people were debating who the next bishop would be, a child cried out, that, Ambrose should be, and he soon was.
Now all of this has been mentioned in a book by Joseph F. O'Callaghan, Electing our bishops: how the Catholic Church should choose its leaders. I knew the stories of the elections of Fabian, and Ambrose as a child. My father, who went to two years of school in the old country, had told me, and his family had been clericalists; but he knew the most ancient of some of the Slavs were pure democrats who embodied the social contract.‡
*Epistle LXXIII. To Pompey... paragraph x.
“Not given to wine, no striker, but modest, not quarrelsome, not covetous, but” — I Timothy iii. 3.
“For a bishop must be without crime, as the steward of God: not proud, not subject to anger, not given to wine, no striker, not greedy of filthy lucre: But given to hospitality, gentle, sober, just, holy, continent: Embracing that faithful word which is according to doctrine, that he may be able to exhort in sound doctrine, and to convince the gainsayers.” — Titus i. 7-9.
**Epistle LXVII. ....concerning Basilides and Martial. paragraph iii. ‡Method for the Easy Understanding of History, 1566, Six livres de la Republique Paris, 1576. Also written earlier, a chronicle by John of Viktring (Johannes Victoriensis, Abbot of Viktring/Vetrinj), †1347, Liber certarum historiarum.