Rapscallion's initially suspicious about politician (5)
I believe the answer is:
scamp
'rapscallion's' is the definition.
(synonyms)
'initially suspicious about politician' is the wordplay.
'initially' indicates taking the first letters.
'about' becomes 'ca' (abbreviation for circa).
'politician' becomes 'MP' (Member of Parliament).
The initial letter of 'suspicious' is 's'.
's'+'ca'+'mp'='SCAMP'
(Other definitions for scamp that I've seen before include "Scallywag" , "Mischief-maker" , "Impish child" , "A young rascal misbehaving in camps" , "Tearaway" .)