Democrat supporting battle for part of constituency (4)
I believe the answer is:
ward
'part of constituency' is the definition.
(type of electoral division)
'democrat supporting battle' is the wordplay.
'democrat' becomes 'd'.
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'battle' becomes 'war' (I've seen this before**).
'd' after 'war' is 'WARD'.
'for' is the link.
(Other definitions for ward that I've seen before include "Child taken care of" , "Minor with guardian - division of city" , "Minor in the charge of a guardian" , "Doctor in 5A 1D [PROFUMO AFFAIR]" , "Hospital room with beds" .)