A Republican opponent makes an appearance (7)
I believe the answer is:
arrival
'an appearance' is the definition.
(to appear can mean to arrive at a particular place)
'a republican opponent' is the wordplay.
'republican' becomes 'r' (abbreviation).
'opponent' becomes 'rival' (a rival is an opponent or enemy).
'a'+'r'+'rival'='ARRIVAL'
'makes' is the link.
(Other definitions for arrival that I've seen before include "Advent" , "The A in ETA" , "Appearance, entrance" , "Someone who's just come" , "Achievement of destination" .)