The question isn't really about Trump being a Christian. The question is about whether or not the Pope and Papacy are Christian.
The place in the Bible that the Roman Catholic Church uses as its excuse for the Papacy is Matthew 16:16-19:
16 Simon Peter answered, “You are the Christ, the Son of the living God.”
17 Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by man, but by my Father in heaven.
18 And I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it.
19 I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.”
Looks like they might be right. But other people say that Jesus was referring to Peter only when Peter expressed Jesus salvation. Are they right when they say this? Might it be that Peter is not the first Pope after all? Look what happens directly after the above Bible quote. From Matthew 16:21-23:
21 From that time on Jesus began to explain to his disciples that he must go to Jerusalem and suffer many things at the hands of the elders, chief priests and teachers of the law, and that he must be killed and on the third day be raised to life.
22 Peter took him aside and began to rebuke him. “Never, Lord!” he said. “This shall never happen to you!”
23 Jesus turned and said to Peter, “Get behind me, Satan! You are a stumbling block to me; you do not have in mind the things of God, but the things of men.”
Now we see. The Papacy is based on Satan. The Pope is the anti-Christ that is predicted in several places in the New Testament, especially in the Revelation.
There is more N.T. explanation the shows that this is so. Even the O.T. has some clarification in a few places showing this to be true. MakingMoneyHoney pointed out one time, the place that says that when the Pope comes in His own name, and claims to be from God, that this is the sign of the anti-Christ.
Anyone who sets himself in the place of God is the anti-Christ. The Pope fits this description. But people always want a king other than God. In this case, their king, the Pope, is dragging them away from salvation.
Trump's few mistakes here and there are nothing when compared with the lies of the Pope and Papacy.