Mockery of politician in debate that hasn't succeeded (8)
I believe the answer is:
contempt
'mockery' is the definition.
(thesaurus)
'politician in debate that hasn't succeeded' is the wordplay.
'politician' becomes 'mp'.
'in' indicates putting letters inside.
'debate' becomes 'contest'.
'that hasn't' indicates named letters should be taken away.
'succeeded' becomes 's' (genealogical abbreviation).
'mp' placed inside 'contest' is 'contesmpt'.
'contesmpt' with 's' taken away is 'CONTEMPT'.
'of' acts as a link.
(Other definitions for contempt that I've seen before include "Beneath this is despicable" , "Disdain or disrespect, perhaps or court" , "Scorn; disgrace" , "The feeling of despising someone" , "In which you may be held" .)