Foolishness of US leader once, really losing head (8)
I believe the answer is:
trumpery
'foolishness of us leader' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'once really losing head' is the wordplay.
'once' becomes 'trump' (I can't justify this - if you can you should believe this answer much more).
'really' becomes 'very' (I've seen this in other clues).
'losing head' means to remove the first letter.
'very' with its initial letter taken away is 'ery'.
'trump'+'ery'='TRUMPERY'
Can you help me to learn more?
(Other definitions for trumpery that I've seen before include "Practices or beliefs of little worth" , "Foolish, worthless talk or actions" , "Worthless trinkets" , "Worthless (thing)" , "Twaddle" .)