Elected one-time whistle-blower (8)
I believe the answer is:
informer
'whistle-blower' is the definition.
(thesaurus)
'elected one-time' is the wordplay.
'elected' becomes 'in'.
'one-time' becomes 'former' (I've seen this before).
'in'+'former'='INFORMER'
(Other definitions for informer that I've seen before include "stoolie" , "Whistle-blower" , "He gives incriminating data about others to the police" , "sneak" , "spy" .)