Background to that man's politician (7)
I believe the answer is:
history
'background' is the definition.
(thesaurus)
'that man's politician' is the wordplay.
'that man's' becomes 'his' (I've seen this before).
'politician' becomes 'tory' (I've seen this before).
'his'+'tory'='HISTORY'
'to' is the link.
(Other definitions for history that I've seen before include "Background" , "Account of past events" , "Old record" , "Time passed" , "'... repeats itself'" .)