Regressive retribution consumes a Republican (8)
I believe the answer is:
rearward
'regressive' is the definition.
(going backwards or to the rear)
'retribution consumes a republican' is the wordplay.
'retribution' becomes 'reward' (retribution can mean one's reward).
'consumes' indicates putting letters inside.
'republican' becomes 'R' (abbreviation in US politics).
'a'+'r'='ar'
'reward' placed around 'ar' is 'REARWARD'.
(Other definitions for rearward that I've seen before include "Towards the back" , "Toward the back" .)