Supporter to remain (4)
I believe the answer is:
stay
This clue is a double definition.
'supporter' is the first definition.
(I've seen this before)
'remain' is the second definition.
(synonyms)
'to' is the link.
(Other definitions for stay that I've seen before include "Abide" , "Board; continue" , "Defer" , "Supporter" , "Stop; support" .)