Right let in extreme nationalists, initially (4)
I believe the answer is:
lien
'right' is the definition.
(legal right)
'let in extreme nationalists initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'let in extreme nationalists' is 'LIEN'.
(Other definitions for lien that I've seen before include "Security for a debt" , "Legal right over the Nile" , "The right to take property if an obligation is not discharged" , "Right to keep property" , "Right to another's property, if an obligation is not discharged" .)