If... when the anti christ comes on the scene, an impostor, posing as Jesus.... why then is it a shocker when he later claims to be God? It would seem that if he were posing as the Christ of today's Christians, that he would not need to claim to be God but rather be assumed to be God? The Christ of today's Christians has already claimed to be God. Hmmmm
I would agree that when he comes and claims to be Jesus, the ones who believe that would also believe he is God under the Trinitarian or Oneness belief.
Does scripture say he will claim to be Christ at first and then later claim to be God? If so then that would dispute the Trinity and Oneness belief.