Influence of wise leader within state (4)
I believe the answer is:
sway
'influence' is the definition.
(swaying is a kind of influencing)
'wise leader within state' is the wordplay.
'leader' suggests taking the first letters.
'within' means one lot of letters goes inside another.
'state' becomes 'say' ('say' can be a synonym of 'state'**).
The first letter of 'wise' is 'w'.
'w' inserted into 'say' is 'SWAY'.
'of' is the link.
(Other definitions for sway that I've seen before include "Ways to waver in opinion or posture" , "Influence; dominance" , "Move gently" , "Swing from side to side, or influence opinion" , "Oscillate" .)