Benefactor's party rounding on Republican (5)
I believe the answer is:
donor
'benefactor's' is the definition.
(donor is a kind of benefactor)
'party rounding on republican' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'rounding' indicates anagramming the letters (I've seen 'round' mean this).
'republican' becomes 'r' (abbreviation).
'on'+'r'='onr'
'onr' anagrammed gives 'nor'.
'do'+'nor'='DONOR'
(Other definitions for donor that I've seen before include "One who dishes out" , "One who gives, maybe blood" , "A giver, perhaps of blood" , "blessed person, relatively" , "Someone providing" .)