Leaving platform, politician's first to show hatred (5)
I believe the answer is:
odium
'hatred' is the definition.
(odium is a kind of hatred)
'leaving platform politician's first' is the wordplay.
'leaving' is a deletion indicator.
'platform' becomes 'podium' (podium is a kind of platform).
'politician's first' becomes 'p' (1st letter of 'politician').
'podium' with 'p' taken away is 'ODIUM'.
'to show' is the link.
(Other definitions for odium that I've seen before include "Hatred, repugnance" , "Great hatred." , "Dislike of someone, or something hated" , "disapprobation" , "Widespread dislike and contempt" .)