Stop using campaign item about Republican rumour (6)
I believe the answer is:
canard
'rumour' is the definition.
(a canard is a false rumour or story)
'stop using campaign item about republican' is the wordplay.
'stop using' becomes 'can' (can can mean to cancel or suspend).
'campaign item' becomes 'ad' (advertising campaign).
'about' is an insertion indicator.
'republican' becomes 'r' (abbreviation).
'ad' enclosing 'r' is 'ard'.
'can'+'ard'='CANARD'
(Other definitions for canard that I've seen before include "False rumour, originally from France" , "Unfounded rumour or story" , "A French kind of false rumour" , "False rumour - French duck" , "Baseless rumour" .)