Responsibility of working American (4)
I believe the answer is:
onus
'responsibility' is the definition.
(thesaurus)
'working american' is the wordplay.
'working' becomes 'on'.
'american' becomes 'us'.
'on'+'us'='ONUS'
'of' acts as a link.
(Other definitions for onus that I've seen before include "Burden, duty" , "'Burden, load (4)'" , "Obligation - charge" , "Encumbrance" , "Weight of responsibility" .)