Working American’s responsibility (4)
I believe the answer is:
onus
'responsibility' is the definition.
(onus is a duty or responsibility)
'working american's' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'american' becomes 'us' (abbreviation for United States).
'on'+'us'='ONUS'
(Other definitions for onus that I've seen before include "albatross?" , "Burden, duty" , "Duty or responsibility" , "'Burden, load (4)'" , "Liability" .)