One hopeful partisan in action (8)
I believe the answer is:
aspirant
'one hopeful' is the definition.
(synonyms)
'partisan in action' is the wordplay.
'in action' indicates anagramming the letters (I've seen this in other clues).
'partisan' is an anagram of 'ASPIRANT'.
(Other definitions for aspirant that I've seen before include "Partisan sort of hopeful" , "Partisan (anag)" , "One with ambition" , "Hopeful, wannabe" , "pretender" .)