To me, the first sign that someone knows deep in their heart their position is unsustainable and unsupportable is when they refuse to discuss it and just state over and over what their position is, or state it and leave. In this case, he appears to be one of those that Cain is always accusing us of being: an Alt-Right leaning person claiming to be a Conservative.
There are peaceful Muslims and extremist Muslims, same as their are peaceful Christians and extremist Christians . It's the extremists that are the issue and they must be prosecuted to the full extent of the law, no matter what the religion they use to justify their violence.
Yes, the founding fathers were concerned about a situation like the Church of England when writing Constitution. However, I feel they should have been well aware of the Muslims and their religion since the crusades were nearly 600 years before. If they had desired that only Christianity be allowed in the nation, I think they would have included that. They did not.
Does my Christianity sometimes conflict with my being an American? Yep. However, one of the basics of Christianity is the freedom to reject it if you desire without issue on this world, your judgement will be in the next. Because of this, I want to fall on the side of Freedom.