Mormons are not Christians. To the extent that they have a coherent belief system, at least half of it goes directly against orthodox Christian beliefs as codified in the Nicene Creed.
First and foremost, they believe that "god" was once a man like us, who was "exalted" to godhood by living a good Mormon life. Further, they believe that each of them can also become a god after death, creating their own little universe and ruling over it the same way that God rules our universe.
Sound Christian to you?
As an outsider, the only thing I care about w/r/t Mormons (they don't like to be called that) is whether they live law-abiding lives, fend for themselves, and do civic-minded stuff, which they appear to do more than most groups.
"White supremacist" is a term that has lost all meaning in recent times. I am one, by most definitions. If used as a slander, it is meaningless.