Perfect popular diplomacy (6)
I believe the answer is:
intact
'perfect' is the definition.
(I've seen this before)
'popular diplomacy' is the wordplay.
'popular' becomes 'in'.
'diplomacy' becomes 'tact' (I've seen this before).
'in'+'tact'='INTACT'
(Other definitions for intact that I've seen before include "Not broken or damaged" , "Not damaged in any way" , "Undiminished" , "Undamaged, unimpaired" , "Not damaged or missing a part" .)