Both groups undoubtedly are Christians. Catholicism as a Christian set was around long before Protestantism so has a better claim in some ways to being seen as Christians.
My view of Mormons is somewhat coloured. I personally believe that Mormonism is an extension of that mindset that likes to believe that someone in a given nation state invented everything. We all have them in each country, people who feel that someone in their country was first to invent this and create that. The only thing those in AMerica couldnt claim ownership of was the Biblical story and Christianity as a religious faith. So someone had the "bright" idea of saying "whilst that was going on in Israel we had out own version here".
It is an oddity. I am an atheist because from where I'm sitting I see no evidence for God and no desire to like him/her even if there is one based on the way some sections of Christianity present their God. If there is a God, a divine creator, I'd like to think he/she was above such petty human emotions like jealousy, bigotry and segregation which it seems are the corner stone of what many Christians believe their God is at heart.