Every religion is allowed to have members run for public office. Catholics, Protestants, Mormons, Scientologists, Kali death cult members, Voodoo priests, Communist atheists, you name it, they are allowed to run.
That isn't the issue.
The issue is how we, as voters, can select candidates whose beliefs are most in alignment with our own, and who we judge to be most likely to perform their offices in a manner that we will like.
As such, ANY quality or attribute of the candidate is a valid subject for consideration in making that evaluation: religion, race, ethnicity, political ideology, whatever.
If I decide his religious beliefs will make him act counter to what I desire, then that is a factor.
If I judge his race will be a factor, in the sense of having more loyalty or favoritism to fellow members than to those not of his race, then that will be a factor.
If I decide his ideology is counter to the direction I want the country to go in, then that will be a factor.
I'll bet the JW's have a different take on this...