US president (5)
'us president' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for obama that I've seen before include "Trump's predecessor" , "one with top job in Washington" , "in the White House" , "American president" , "US president born in Hawaii" .)
(Other definitions for washington that I've seen before include "US capital" , "Tree feller of myth" , "First US president" , "Old president" , "Irving" .)
(Other definitions for clinton that I've seen before include "Former US president" , "Chelsea?" , "Forty second US president" , "Statesman" , "US president from 1993" .)
(Other definitions for truman that I've seen before include "- - Capote (lit.)" , "Harry S. ---, US Pres." , "US president, 1945-53" , "Harry S ..., former president of USA" , "Harry S ...... was USA president 1945-53" .)