To me racism and xenophobia are the the things that fuelled the actual Holocaust. I tried to outline some of the racism inherent to Trump further up.
To be honest, I don't understand conservative Christians love for republicans. They preach social darwinism, often they preach fear of others. Is it all based on this notion that "The left also treats Christians with disdain"?
My view of Christianity (I come from a more Lutheran view...) is one of 'love thy neighbor' and charity towards the poor as the guiding principles. I consider myself a humanist, but understand that my flavor of Western humanism is essentially the non-secular continuation of Christian values -- which are inherently compatible with leftist values that are also very much based on compassion and empathy. This all seems to be incompatible with the hatefulness I see from republicans, especially somebody like Trump. To me, Trump is a selfish nihilist.
One of my favorite Presidents is Jimmy Carter, and his strong moral center based on religious beliefs is the main reason.