Realise social security covers America (4)
I believe the answer is:
suss
'realise' is the definition.
(I've seen this before)
'social security covers america' is the wordplay.
'social security' becomes 'SS' (abbreviation).
'covers' indicates putting letters inside.
'america' becomes 'US' (abbreviation for the United States).
'ss' enclosing 'us' is 'SUSS'.
(Other definitions for suss that I've seen before include "sharpness of mind" , "Work (out) (slang)" , "Discover (something out)" , "Divine nature of" , "Check out" .)