Oh...I don’t think the Trininty is 4th century at all.
I think it is one of many polytheistic seductions that have been around since Lucifer was kicked out of heaven.
For the record, the rabbis have always understood the Sh'khinah, the Divine Presence, and the Holy Spirit to be simultaneously of God and sent from God. They teach that the Torah is God's wisdom (thus, an attribute of the Holy One rather than a creation) which was with Him in the beginning and which He used to create the universe. The Talmud and other rabbinic sources frequently portray conversations between the Holy One and the Sh'khinah, or the Holy One and the Torah. And yet we still affirm, HaShem Echad.
Your "polytheism" charge betrays an ignorance of Christianity's Jewish roots. It also betrays a lack of understanding in Scripture. The Glory (Kevod) of God filled the Holy Place from the days of Moses to the days of Ezekiel. Does that mean that God was not on His throne in Heaven?
Shalom.