Do some tremendous campaigning (4)
I believe the answer is:
scam
'do' is the definition.
(I've seen this before)
'some tremendous campaigning' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'SCAM' can be found hidden inside 'tremendous campaigning'.
(Other definitions for scam that I've seen before include "Confidence trick, swindle" , "Rip off" , "Racket" , "Fraudulent trick or swindle" , "Dubious operation" .)