A politician in bluster's out of control (7)
I believe the answer is:
rampant
'out of control' is the definition.
(thesaurus)
'a politician in bluster's' is the wordplay.
'politician' becomes 'mp'.
'in' is an insertion indicator.
'bluster' becomes 'rant'.
'a'+'mp'='amp'
'amp' inserted inside 'rant' is 'RAMPANT'.
(Other definitions for rampant that I've seen before include "Showing unrestrained growth" , "Fulminate" , "Out of control" , "Unrestrained, flourishing excessively" , "Growing or spreading uncontrollably" .)