In US, smart retreat by black political leader (4,5)
I believe the answer is:
tony blair
'political leader' is the definition.
'in us smart retreat by black' is the wordplay.
'in us smart' becomes 'tony' (US term meaning fashionable).
'retreat' becomes 'lair' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'black' becomes 'b' (as in pencil classifications).
'lair' put after 'b' is 'blair'.
'tony'+'blair'='TONY BLAIR'
(Other definitions for tony blair that I've seen before include "Middle East envoy" , "Politician - Tory in Lab (anag)" , "Prime Minister of the UK" .)