Success with Government faction (4)
I believe the answer is:
wing
'faction' is the definition.
(a group within an organisation)
'success with government' is the wordplay.
'success' becomes 'win' (I've seen this in another clue).
'with' says to put letters next to each other.
'government' becomes 'g' (abbreviation for government).
'win'+'g'='WING'
(Other definitions for wing that I've seen before include "bit of a mansion" , "Branch (of a hospital building etc)" , "Projecting part of bird or aircraft" , "Wound, but not fatally" , "Pinion" .)