Rancour with current politics half vanishing in campaign (9)
I believe the answer is:
gallipoli
'in campaign' is the definition.
(I've seen this before)
'rancour with current politics half vanishing' is the wordplay.
'rancour' becomes 'gall' (gall can mean rancour or resentment).
'with' says to put letters next to each other.
'current' becomes 'I' (symbol for electric current).
'half vanishing' indicates taking half.
'politics' cut in half is 'poli'.
'gall'+'i'+'poli'='GALLIPOLI'
(Other definitions for gallipoli that I've seen before include "battle site" , "Long ago landing" , "Turkish town" , "part of Turkey" , "Turkish scene of WW1 landing" .)