Religion and Politics do not mix for the simple reason that it can get in the way of what people want and if the state is listening to what people want and legislating accordingly then clearly religion is something that in these modern times has no place in Politics.
People want to live in 'sin' ie together without marriage, multiple sexual partners and so on.
Meanwhile, which religion's rules should be applied or adopted, whose God should be worshipped?
Athiests believe in one less God than most religious people and yet they are looked down upon by those who deny all Gods except their own. Most religions as far as I can tell have similar moral codes, thus these are pretty much societal norms and any decent government is wise to heed them regardless of whether these codes are promoted under the umbrella of religion or not.
We all agree 'thou shalt not kill'
We all agree 'thou shalt honour they mother and father' and so on.
There is a lot of common ground there. This is where the emphasis should be rather than on any individual religion. Also settling for any specific religion would alienate much of the voting public and so not the wisest move for any wanabee candidate. Atheism is growing as are alternative religions. Selecting one above others to represent a Political view point could lead to accusations of discrimination.
Candidates who are religious would be wise to try not to let their beliefs affect their decision making. For example, should a Catholic Prime Minister/President decide to make abortion illegal the ramifications would be far reaching, despite the fact many of us believe this is immoral whether we be religious or not, we cannot legislate on a 'belief' when there are 'real life' factors which require serious consideration before any decision is made.
There are countries today that have Political systems based on religious beliefs, consider Sharia law in some Arab countries. Is this really the way we want to go?