With this burden, you'll never get off to America (4)
I believe the answer is:
onus
'with this burden you'll never' is the definition.
'onus' can be an answer for 'burden' (synonyms). I am not sure about the remainder of the definition.
'off to america' is the wordplay.
'off' becomes 'on' (I can't justify this - if you can you should give a lot more credence to this answer).
'to america' becomes 'US' (United States).
'on'+'us'='ONUS'
'get' acts as a link.
Can you help me to learn more?
(Other definitions for onus that I've seen before include "Responsibilty" , "'Responsibility, task or burden (4)'" , "Burden, duty" , "'Burden, of proof (4)'" , "Duty or responsibility" .)