One politician goes rogue (3)
I believe the answer is:
imp
'rogue' is the definition.
(thesaurus)
'one politician' is the wordplay.
'one' becomes 'i' (Roman numeral).
'politician' becomes 'MP' (Member of Parliament).
'i'+'mp'='IMP'
'goes' is the link.
(Other definitions for imp that I've seen before include "pickle" , "Mischievous child" , "Emperor" , "Small demon" , "old-fashioned graft" .)