Campaigning is never about displaying flag (6)
I believe the answer is:
ensign
'flag' is the definition.
(ensign is a kind of flag)
'campaigning is never about displaying' is the wordplay.
'displaying' indicates the answer is hidden within the clue.
'about' says the letters should be written in reverse.
'ngisne' can be found hidden inside 'campaigning is never'.
'ngisne' written backwards gives 'ENSIGN'.
(Other definitions for ensign that I've seen before include "National flag" , "that's flown" , "officer in the US navy" , "Ship's colours" , "Small flag or junior naval officer" .)