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 not sure about the 'agents' singular' bit.
'against us immigration' is the wordplay.
'against' becomes 'v' (versus).
'us immigration' becomes 'ices' (I am not sure about this - if you are sure you should believe this answer much more).
'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" .)