Brief strain troubled politician (10)
I believe the answer is:
transitory
'brief' is the definition.
(I've seen this before)
'strain troubled politician' is the wordplay.
'troubled' indicates an anagram.
'politician' becomes 'tory' (I've seen this before).
'strain' with letters rearranged gives 'transi'.
'transi'+'tory'='TRANSITORY'
(Other definitions for transitory that I've seen before include "Brief" , "Short-lived" , "Here-today-gone-tomorrow" , "Fleeting" , "Ephemeral" .)