One might call himself a Christian while maintaining a non-Trinitarian stance, but it is utterly impossible to be a Christian unless you can, in one form or another, be able to affirm the following:
We believe in one God the Father all-powerful, maker of heaven and of earth, and of all things both seen and unseen. And in one Lord Jesus Christ, the only-begotten Son of God, begotten from the Father before all the ages, light from light, true God from true God, begotten not made, consubstantial with the Father, through whom all things came to be; for us humans and for our salvation he came down from the heavens and became incarnate from the holy Spirit and the virgin Mary, became human and was crucified on our behalf under Pontius Pilate; he suffered and was buried and rose up on the third day in accordance with the scriptures; and he went up into the heavens and is seated at the Father's right hand; he is coming again with glory to judge the living and the dead; his kingdom will have no end. And in the Spirit, the holy, the lordly and life-giving one, proceeding forth from the Father, co-worshipped and co-glorified with Father and Son, the one who spoke through the prophets; in one, holy, catholic and apostolic church. We confess one baptism for the forgiving of sins. We look forward to a resurrection of the dead and life in the age to come. Amen.
Canon 1 of the second Ecumenical council states: The profession of faith of the holy fathers who gathered in Nicaea in Bithynia is not to be abrogated, but it is to remain in force. Every heresy is to be anathematised and in particular that of the Eunomians or Anomoeans, that of the Arians or Eudoxians, that of the Semi-Arians or Pneumatomachi, that of the Sabellians that of the Marcellians, that of the Photinians and that of the Apollinarians.
The above is not optional (although translations will vary, of course). It is also not exclusively a "Catholic" thing (as far as the Church in communion with the See of Peter), it is not exclusively an Orthodox thing, to my knowledge, with the exception of some new ecclesial communities that have come up in the past century or two (such as the Mormons, oneness Pentecostals, and JWs), this is something that is accepted universally.
And in the Spirit, the holy, the lordly and life-giving one, proceeding forth from the Father, co-worshipped and co-glorified with Father and Son, the one who spoke through the prophets; in one, holy, catholic and apostolic church. We confess one baptism for the forgiving of sins. We look forward to a resurrection of the dead and life in the age to come. Amen.
Sure...Teddy Kennedy professed that...Ms Pelosi claims that...
FACT is: you don't have to know much of anything to become a Christian and if you put baptism and a Church between you and Jesus, you'll likely never will become a Christian...