Rose, perhaps, for former president (4)
I believe the answer is:
This clue is a double definition.
'rose perhaps' is the first definition.
(rose is a kind of bush)
'former president' is the second definition.
(either of the George Bushes)
'for' acts as a link.
(Other definitions for bush that I've seen before include "A shrub or a modern president" , "Shrub; wild vegetation" , "Shrub; hole lining" , "Rural African" , "metal sleeve used in drilling" .)