Behind Republican listener (4)
I believe the answer is:
rear
'behind' is the definition.
(both can mean one's bottom)
'republican listener' is the wordplay.
'republican' becomes 'r' (abbreviation).
'listener' becomes 'ear' (body part which hears or listens).
'r'+'ear'='REAR'
(Other definitions for rear that I've seen before include "Rump" , "The back part of something" , "Bring up - back end" , "Breed or bring up" , "Hind part" .)