Awful strain in the lead up to politician's passing (10)
I believe the answer is:
transitory
'passing' is the definition.
(I've seen this before)
'awful strain in the lead up to politician's' is the wordplay.
'awful' indicates an anagram.
'in the lead up to' means one lot of letters go next to another.
'politician' becomes 'tory' (I've seen this before).
'strain' is an anagram of 'transi'.
'transi'+'tory'='TRANSITORY'
(Other definitions for transitory that I've seen before include "Ephemeral" , "lasting long" , "Short-lived" , "Passing" , "Brief" .)