It may the official doctrine of most Christians, but how many of the members actually still believe in the Trinity? I never did, nor will I ever. God in three persons is not consistent with the idea of One God (in which I don't believe, by the way), IMO. I am also not aware that it can be found in the Hebrew (aka Old) Testament, which it would be if it were a basic truth.
In my opinion, the strongest case for the Trinity being present in the OT has to be in Genesis 18 when God visits Abraham near Marne shortly before destroying Sodom and Gomorrah. Personally, I think the three visitors are a remnant of the polytheistic past that managed to not get totally expunged when the monotheistic editors of the Pentateuch were writing down the Hebrew mythos for their use, but I can see it being a case for the Trinity.
