Through defending American government, Republican is an enabler of Congress (6)
I believe the answer is:
viagra
'an enabler of congress' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'through defending american government republican' is the wordplay.
'through' becomes 'via' (via means going through).
'defending' is an insertion indicator (inserted letters are defended).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'government' becomes 'g' (abbreviation for government).
'republican' becomes 'r' (abbreviation).
'a'+'g'+'r'='agr'
'via' enclosing 'agr' is 'VIAGRA'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for viagra that I've seen before include "Drug aiding one's sex life" , "Controversial pills" , "Male sexual aid" , "Performance-enhancing drug?" , "Drug to improve potency" .)