The burden of working with American (4)
I believe the answer is:
onus
'the burden' is the definition.
('onus' can be a synonym of 'burden')
'working with american' is the wordplay.
'working' becomes 'on'.
'with' is a charade indicator (letters next to each other).
'american' becomes 'us'.
'on'+'us'='ONUS'
'of' acts as a link.
(Other definitions for onus that I've seen before include "Capulet opponent (R&J)" , "Weight of responsibility" , "'Burden, of proof (4)'" , "Burden, duty" , "Liability" .)