Chaim:
...there is no evidence Jews before Jesus ever thought in Trinitarian terms. Ergo, Jesus as part of a Godhead would be a god they and their fathers never knew - and as any other god, would rightly be rejected.

Medini:
Just to second Chaim's statement above, and add that not only is there no evidence that Jews before JC or at JC's supposed time ever thought of G-d in Trinitarian terms, BUT there is hard evidence that they, in fact, understood G-d as Echad in the sense of Absolutely SIMPLE Unity - I have already cited the Sefer Yetzirah (written by R. Akiva so within a century of JC's supposed date but containing teachings that go back all the way to Avraham) in this regard about G-d: "In the presence of One, what can you count?" (a One in which there is no plurality and no participation in plurality), but I also cite the "non-Rabbinic" Philo - an older contemporary of JC (assuming he lived): "G-d is alone, a unity in the sense that His nature is simple" (His Oneness = Simplicity, not any kind of "complex unity").