Stood up as former American president can be a bit prickly (8)
I believe the answer is:
rosebush
'former american president can be a bit prickly' is the definition.
I can't judge whether this defines the answer.
'stood up' is the wordplay.
'stood' becomes 'rose' (rose up).
'up' becomes 'bush' (I can't justify this - if you can you should believe this answer much more).
'rose'+'bush'='ROSEBUSH'
'as' is the link.
Can you help me to learn more?
(Other definitions for rosebush that I've seen before include "Thorny growth" , "Plant" , "Flower supplier" , "shrub" .)