I believe it's important to understand why people assume as a premise that Jesus is God, and whether this had always been the held belief.
Was the belief that Jesus is God maintained in the oldest Christian dissertations? (The Divine Trinity, by Joseph Pohle, Rt. Rev. Msgr., p. 150)
“[…] the Didache, or ‘Teaching of the Twelve Apostles,’ the oldest
literary monument of Christian antiquity outside of the New Testament
canon, […] contains no formal profession of faith in the Divinity of
Jesus Christ and the Atonement.”
What does the Didache not contain? "[a] formal profession of faith in the Divinity of Jesus Christ." Hence, such a belief was not yet held in the First Century.
When the Second Century came, who was the first to deify Jesus? (Systematic Theology, by Augustus H. Strong, D.D., L.L.D., p. 305)
“The earliest time known at which Jesus was deified was, after the New
Testament writers, in the letters of Ignatius, at the beginning of the
second century.”
Who was the first to deify Jesus? "Ignatius". However, this did not catch on immediately.
At the turn of the third century, what happened, which is why the idea eventually caught on? (The Faith of Millions, by John A. O'Brien, Ph.D., p. 99)
“Thus, Celsus, a scoffing pagan philosopher of the third century,
contended that […] worship of Christ was essentially polytheistic. […]
Origen, the greatest of the early Christian writers, defended the
Christians […] by showing that the Savior was worthy of such adoration
because He was God.”
What did a pagan philosopher by the name of Celsus accuse the Christians of? "worship of Christ was essentially polytheistic". How did a Christian writer by the name of Origin counter this? "by showing that the Savior was worthy of such adoration because He was God."
In truth, why do we worship and bow at Jesus' name, according to the Scriptures? (Phil. 2:9-11)
"Therefore God also has highly exalted Him and given Him the name
which is above every name, that at the name of Jesus every knee should
bow, of those in heaven, and of those on earth, and of those under the
earth, and that every tongue should confess that Jesus Christ is Lord,
to the glory of God the Father."
What do we bow down to? Paul said, "the name of Jesus". Who gave Jesus this name? Paul explained, "God also has highly exalted Him and given Him the name". Hence, we worship Jesus not because He is God, but because this is the will of God.
Who is the God who is glorified when we follow this will? Paul said, "the Father".
Thus, by the turn of the Fourth Century, had everyone accepted the premise the Jesus is God? (The Philosophy of the Church Fathers, by Harry A. Wolfson, Vol. 1, p. 306)
“[…] as late as the fourth century there were those within
Christianity who […] still argued against the divinity of the
preexistent Christ”
What was still being argued against? "the divinity of the preexistent Christ".
Who was among the most vocal? (Ancient and Medieval History, by Ralph Magoffin, V.D., p. 394)
“A priest in Alexandria named Arius […] said that if God and the Son
were both divine, then there were two gods, which meant that
Christianity was not a monotheistic religion,”
Who argued against the divinity of Christ? "A priest in Alexandria named Arius".
Who responded to the growing dispute? (Christianity Through the Centuries, by Earle E. Cairns, p. 143-144)
“In 318 or 319, Alexander, the bishop of Alexandria, discussed with
his presbyters ‘The Unity of the Trinity.’ One of the presbyters,
Arius, […] backed by Eusebius of Nicomedia (to be disinguished from
Eusebius of Caesarea) and a minority of those present, insisted that
Christ […] was not coequal, coeternal or cosubstantial with the
Father. […] Constantine then called a council of the bishops of the
Church to work out a solution to the dispute. This council met at
Nicaea in the early summer of 325.”
Who responded to the growing dispute? "Constantine". This was the emperor at the time.
What did he call for? "a council of the bishops of the Church to work out a solution to the dispute."
What was Constantine's goal? (When Jesus Became God, by Richard E. Rubenstein, p. 46)
“Constantine was far too canny […] His true goal, beyond favoring his
co-religionists, was to unite the empire’s diverse, quarreling peoples
in one huge spiritual fellowship. […] Constantine’s advisors called
his attention to a situation that appeared to jeaporize all these
dreams. Its locale, not surprisingly, was that seedbed of religious
controversy, Alexandria […] Clearly something should be done to
investigate the case and formulate a sensible policy to resolve the
conflict.”
What was Constantine's goal? "to unite the empire's diverse, quarreling peoples in one huge spiritual fellowship." Hence, his motivations were not to ascertain the truth, but purely political.
What "truth" did Constantine personally believe in? (The Jesus Establishment, by Johannes Lehmann, p. 173-174)
“The victor at Nicaea was not the Church, but an Emperor who believed
in the sun god as one of several deities,”
What did Constantine personally believe in? "several deities". Constantine was polytheistic.
As such, what did Constantine insist that all present at the council should endorse? (The Jesus Establishment, by Johannes Lehmann, p. 173)
“This is what happened at Nicaea. Some six weeks after the Council
opened, on June 19, 325, Emperor Constantine insisted that all bishops
who had been present should endorse a new creed that confirmed Christ
as God and condemned Arius. Anyone who did not sign this document was
to be excommunicated and exiled.”
What did Constantine insist upon by pain of excommunication? "a new creed that confirmed Christ as God."
What was any Christian who argued against this accused of? (The Emerging Church, Ronald J. Wilkins, p. 110)
“Once this ‘Nicene Creed’ had been publicly signed by all the bishops
and promulgated by Constantine, it became the official creed for all
Christians. To deny the divinity of Christ in any way was to put
oneself outside of the Christian community and was a crime against the
state.”
From this point on, what were Christians who argued against the divinity of Christ accused of? "a crime against the state."
When was this? (Discourses on the Apostles' Creed, by Rev. Clement H. Crock, p. 206)
“Thus, for example, it was not until 325 A.D. at the Council of
Nicaea, that the Church defined for us that it was an article of faith
that Jesus is truly God.”
When did the belief that Jesus is truly God become an article of faith that went unchallenged? "not until 325 A.D." This is the reason why people assume as a premise that Jesus is God.