Republican fills in a permit with it (5)
I believe the answer is:
alert
'with it' is the definition.
(I've seen this in another clue)
'republican fills in a permit' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'fills in' indicates putting letters inside.
'permit' becomes 'let' (synonyms).
'a'+'let'='alet'
'r' placed inside 'alet' is 'ALERT'.
(Other definitions for alert that I've seen before include "Put on guard, warn" , "On the ball" , "'Attentive, watchful (5)'" , "Wide-awake and watchful" , "Vigilantly attentive" .)