American party accepting Democrat succeeded makes sense (4,2)
I believe the answer is:
adds up
'makes sense' is the definition.
('add up' can be a synonym of 'make sense')
'american party accepting democrat succeeded' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'party' becomes 'dup' (Democratic Unionist Party).
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'democrat' becomes 'd'.
'succeeded' becomes 's' (genealogical abbreviation).
'd'+'s'='ds'
'dup' enclosing 'ds' is 'ddsup'.
'a'+'ddsup'='ADDS UP'
(Other definitions for adds up that I've seen before include "Sums - makes sense" , "Stands to reason" , "Reckons" , "Tots" , "Puts two and two together" .)