After that, the National Front (4)
I believe the answer is:
then
'after that' is the definition.
('then' can be a synonym of 'after that')
'the national front' is the wordplay.
'front' says to take the initial letters.
The first letter of 'national' is 'n'.
'the'+'n'='THEN'
(Other definitions for then that I've seen before include "At that time; next" , "Consequently" , "Afterwards - as a result" , "soon?" , "Subsequently - previously" .)