Exhaust American power restraining Brussels? (3,2)
I believe the answer is:
use up
'exhaust' is the definition.
(synonyms)
'american power restraining brussels?' is the wordplay.
'american' becomes 'US' (United States).
'power' becomes 'p' (symbol in physics).
'restraining' means one lot of letters goes inside another.
'brussels?' becomes 'EU' (European Parliament is based in Brussels).
'us'+'p'='usp'
'usp' placed around 'eu' is 'USE UP'.
(Other definitions for use up that I've seen before include "Consume (stocks)" , "Entirely consume" , "Finish, exhaust" , "Expend" , "Exhaust (resources)" .)