US politician defending one’s religious faith (5)
I believe the answer is:
deism
'religious faith' is the definition.
(belief in a god)
'us politician defending one's' is the wordplay.
'us politician' becomes 'dem' (short for Democrat).
'defending' is an insertion indicator.
'one's' becomes 'I's' (Roman numeral).
'dem' enclosing 'is' is 'DEISM'.
(Other definitions for deism that I've seen before include "Belief in a creator" , "Belief in a god from reason not revelation" , "Belief in a supreme being who does not intervene in the universe" , "Belief in the existence of God" .)