Responsibility lies in, for one reason, USA (4)
I believe the answer is:
onus
'responsibility' is the definition.
(onus is a duty or responsibility)
'lies in for one reason usa' is the wordplay.
'ONUS' is hidden in amongst the letters.
However, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for onus that I've seen before include "Capulet opponent (R&J)" , "'Burden, of proof (4)'" , "'Burden, load (4)'" , "Weight of responsibility" , "Burden, duty" .)