Always manage without party backing (3,4)
I believe the answer is:
for good
'always' is the definition.
(for good can mean permanently or forever)
'manage without party backing' is the wordplay.
'manage without' becomes 'forgo' (I can't justify this - if you can you should believe this answer much more).
'party' becomes 'do' (do can informally mean a party).
'backing' is a reversal indicator.
'do' in reverse letter order is 'od'.
'forgo'+'od'='FOR GOOD'
Can you help me to learn more?
(Other definitions for for good that I've seen before include "on the side of the angels" , "Informally, once and for all" , "Permanently - that's not bad" , "Permanently, always" , "Purpose of charitable work" .)