Stop Republican going after Democrat and lefties regularly (5)
I believe the answer is:
deter
'stop' is the definition.
(to deter behaviour is to stop it)
'republican going after democrat and lefties regularly' is the wordplay.
'republican' becomes 'R' (abbreviation).
'going after' is a charade indicator (letters next to each other).
'democrat' becomes 'd'.
'and' means one lot of letters go next to another.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'lefties' are 'ete'.
'd'+'ete'='dete'
'r' put after 'dete' is 'DETER'.
(Other definitions for deter that I've seen before include "Prevent by instilling fear" , "Discourage or prevent from doing something" , "Discourage through fear of consequences" , "Cause not to do something" , "Frighten off; prevent" .)