Commie wrong to have moved to the left (4)
I believe the answer is:
trot
'commie' is the definition.
(short for Trotskyite)
'wrong to have moved to the left' is the wordplay.
'wrong' becomes 'tort' (a civil wrong in law).
'to have moved to the left' says the letters should be written backwards (letters written right to left).
'tort' in reverse letter order is 'TROT'.
(Other definitions for trot that I've seen before include "Horse's gait - extreme leftist" , "Move at brisk pace" , "(Horse's) pace faster than a walk" , "Jogging pace" , "movement of H [TROT]" .)