The old king left for the turbulent USA (4)
I believe the answer is:
saul
'the old king' is the definition.
(I've seen this before)
'left for the turbulent usa' is the wordplay.
'left' becomes 'l' (common abbreviation).
'for' means one lot of letters go next to another (I've seen this in other clues).
'the turbulent' indicates an anagram.
'usa' anagrammed gives 'sau'.
'l' put after 'sau' is 'SAUL'.
(Other definitions for saul that I've seen before include "St Paul's name when he started on the road to Damascus" , "Bellow was one" , "Oratorio by Handel" , "inspiring leader of Scots" , "First king of Israel" .)