Doctor hasty to claim unknown politician shows compassion (8)
I believe the answer is:
sympathy
'compassion' is the definition.
(I've seen this before)
'doctor hasty to claim unknown politician' is the wordplay.
'doctor' indicates an anagram.
'to claim' indicates putting letters inside (inserted letters are claimed or taken in).
'unknown' becomes 'y' (algebra).
'politician' becomes 'MP' (Member of Parliament).
'hasty' is an anagram of 'sathy'.
'y'+'mp'='ymp'
'sathy' enclosing 'ymp' is 'SYMPATHY'.
'shows' is the link.
(Other definitions for sympathy that I've seen before include "Fellow-feeling, understanding" , "Fellow-feeling in time of grief" , "An understanding of another's sadness" , "Feeling like another" , "agreement" .)