It’s called “polling” and you should look at some. The word “Mormon” scares a lot of people. I’m not saying it’s logical, I’m just saying it’s a big problem; and the GOP has enough on its plate without taking on that one.
I have seen the polling (whatever it’s worth) and I haven’t seen any that show that mass numbers of people won’t vote for a Mormon. Once the campaign really starts, people will focus more on who he is and less on what denomination he is.