Four in a Republican cartel reaching destination (8)
I believe the answer is:
arriving
'reaching destination' is the definition.
(I've seen this before)
'four in a republican cartel' is the wordplay.
'four' becomes 'iv' (roman numeral).
'in' means one lot of letters goes inside another.
'republican' becomes 'r' (abbreviation).
'cartel' becomes 'ring' (both can mean a criminal group).
'a'+'r'+'ring'='arring'
'iv' placed into 'arring' is 'ARRIVING'.
(Other definitions for arriving that I've seen before include "Reaching a destination" , "Getting there" .)