Remaining Socialist (4)
I believe the answer is:
left
This clue is a double definition.
'remaining' is the first definition.
('left' can be a synonym of 'remaining')
'socialist' is the second definition.
('left' is associated in meaning with 'socialist')
(Other definitions for left that I've seen before include "The sinister side" , "split" , "Socialist direction" , "inclined towards socialism" , "choice at a junction?" .)