Against US immigration agents' singular failings (5)
I believe the answer is:
vices
'agents' singular failings' is the definition.
'vices' can be an answer for 'failings' (I've seen this in another clue). I'm unsure of the 'agents' singular' bit.
'against us immigration' is the wordplay.
'against' becomes 'v' (versus).
'us immigration' becomes 'ices' (I can't justify this - if you can you should give a lot more credence to this answer).
'v'+'ices'='VICES'
Can you help me to learn more?
(Other definitions for vices that I've seen before include "Moral faults or bad habits" , "Sins or depravities" , "Moral weaknesses and holding devices" , "Shortcomings" .)