Unrestrained harangue involving a politician (7)
I believe the answer is:
rampant
'unrestrained' is the definition.
(thesaurus)
'harangue involving a politician' is the wordplay.
'harangue' becomes 'rant' ('rant' can be a synonym of 'harangue').
'involving' is an insertion indicator.
'politician' becomes 'mp'.
'a'+'mp'='amp'
'rant' enclosing 'amp' is 'RAMPANT'.
(Other definitions for rampant that I've seen before include "Unrestrained, flourishing excessively" , "Flourishing excessively as disease may be" , "Growing or spreading uncontrollably" , "Spreading like wildfire" , "Unbridled" .)