Idiot beginning to undermine church in that capacity (2,4)
I believe the answer is:
as such
'in that capacity' is the definition.
(I've seen this in another clue)
'idiot beginning to undermine church' is the wordplay.
'idiot' becomes 'ass' (both can mean a stupid person).
'beginning to' suggests taking the first letters.
'church' becomes 'ch' (common abbreviation).
The first letter of 'undermine' is 'u'.
'ass'+'u'+'ch'='AS SUCH'
(Other definitions for as such that I've seen before include "in a particular capacity" , "in the manner described" , "Intrinsically" , "in that particular role" .)