Responsibility with respect to America (4)
I believe the answer is:
onus
'responsibility' is the definition.
(thesaurus)
'with respect to america' is the wordplay.
'with respect to' becomes 'on'.
'america' becomes 'us' (abbreviation for the United States).
'on'+'us'='ONUS'
(Other definitions for onus that I've seen before include "Duty or responsibility" , "'Responsibility, task or burden (4)'" , "Responsibilty" , "Obligation - charge" , "Burden, duty" .)