A couple of Conservatives exploited the defendant (7)
I believe the answer is:
accused
'the defendant' is the definition.
('accused' can be a synonym of 'defendant')
'a couple of conservatives exploited' is the wordplay.
'couple of' indicates the doubling of some letters.
'conservatives' becomes 'C' (abbreviation in UK politics).
'exploited' becomes 'used' (synonyms).
'c' duplicated is 'cc'.
'a'+'cc'+'used'='ACCUSED'
(Other definitions for accused that I've seen before include "Levelled a charge against" , "Indicted" , "Person being charged" , "Blamed" , "Defendant in a criminal proceeding" .)