President releases model’s derrière (4)
I believe the answer is:
rump
'derriere' is the definition.
(synonyms)
'president releases model's' is the wordplay.
'president' becomes 'trump' (Donald Trump).
'releases' indicates named letters should be taken away.
'model' becomes 't' (Ford Model T car).
'trump' with 't' removed is 'RUMP'.
(Other definitions for rump that I've seen before include "Animal's hind quarters" , "The buttocks or hind-quarters" , "Inferior remains; cut of steak" , "Restricted parliament" , "Backside" .)