Power of wife lying in state (4)
I believe the answer is:
sway
'power' is the definition.
(sway is a kind of power)
'wife lying in state' is the wordplay.
'wife' becomes 'w'.
'lying in' indicates putting letters inside.
'state' becomes 'say' ('say' can be a synonym of 'state'**).
'w' inserted into 'say' is 'SWAY'.
'of' acts as a link.
(Other definitions for sway that I've seen before include "Swing from side to side, or influence opinion" , "Move back and forth" , "Totter; influence" , "Rock to and fro" , "Pitch sideways" .)