Decide roughly about blocking a politician's assistant (4-2-4)
I believe the answer is:
aide-de-camp
'assistant' is the definition.
(thesaurus)
'decide roughly about blocking a politician's' is the subsidiary indication.
'roughly' indicates an anagram.
'about' becomes 'a' (abbreviation in Chambers**).
'blocking' indicates putting letters inside.
'politician' becomes 'mp'.
'decide' with letters rearranged gives 'idedec'.
'idedec'+'a'='idedeca'
'a'+'mp'='amp'
'idedeca' inserted inside 'amp' is 'aidedecamp'.
(Other definitions for aide-de-camp that I've seen before include "Senior officer's assistant" , "Military adviser" , "Military assistant" .)