Abandoned political grouping (4)
I believe the answer is:
left
This clue is a double definition.
'abandoned' is the first definition.
(thesaurus)
'political grouping' is the second definition.
(I've seen this before)
(Other definitions for left that I've seen before include "Went; port" , "Vacated; political wing" , "Withdrew - Labour" , "Allowed to remain" , "political grouping" .)