Dictator's time in power reportedly drops form of control (4)
I believe the answer is:
rein
'form of control' is the definition.
(reins control horses)
'dictator's time in power' is the wordplay.
'dictator's' indicates a 'sounds like' (homophone) clue (as somebody dictating would pronounce the word).
'time in power' becomes 'reign' (eg the reign of a monarch).
'reign' is a homophone of 'REIN'.
'reportedly drops' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for rein that I've seen before include "A means of control" , "Strap on a bridle" , "given free to experienced riders?" , "Director's power" , "Restraining lead" .)