Burden on the States (4)
I believe the answer is:
onus
'burden' is the definition.
('onus' can be a synonym of 'burden')
'on the states' is the wordplay.
'the states' becomes 'us' (abbreviation for the United States).
'on'+'us'='ONUS'
(Other definitions for onus that I've seen before include "Duty or responsibility" , "Capulet opponent (R&J)" , "Obligation - charge" , "'Responsibility, task or burden (4)'" , "Encumbrance" .)