Fool expected to seize power (4)
I believe the answer is:
dupe
'fool' is the definition.
(synonyms)
'expected to seize power' is the wordplay.
'expected' becomes 'due' (similar in meaning).
'to seize' indicates putting letters inside.
'power' becomes 'p' (symbol in physics).
'due' placed around 'p' is 'DUPE'.
(Other definitions for dupe that I've seen before include "A cat's-paw" , "Gull" , "Deceive, trick" , "Victim of deceit or fraud" , "Deceive, make fool of" .)