Politician organised treason (7)
I believe the answer is:
senator
'politician' is the definition.
(I've seen this before)
'organised treason' is the wordplay.
'organised' is an anagram indicator.
'treason' is an anagram of 'SENATOR'.
(Other definitions for senator that I've seen before include "US/Roman politician" , "Member of government" , "Clinton, perhaps" , "Roman legislator" , "US politician" .)