Republican friend in comeback (5)
I believe the answer is:
rally
'comeback' is the definition.
(I've seen this in another clue)
'republican friend' is the wordplay.
'republican' becomes 'r' (abbreviation).
'friend' becomes 'ally' (synonyms).
'r'+'ally'='RALLY'
'in' acts as a link.
(Other definitions for rally that I've seen before include "Revive - motoring contest" , "Regain health" , "Arouse for action" , "Marshal" , "Recover strength after illness" .)