A Republican opponent, he’s got to his destination (7)
I believe the answer is:
arrival
'he's got to his destination' is the definition.
(arrival can mean someone who has arrived)
'a republican opponent' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'opponent' becomes 'rival' (a rival is an opponent or enemy).
'a'+'r'+'rival'='ARRIVAL'
(Other definitions for arrival that I've seen before include "The A in ETA" , "Achievement of destination" , "The reaching of one's destination" , "Advent" , "Appearance (at a destination)" .)