In any case, American is no smarter than anyone else (9)
I believe the answer is:
leastwise
'in any case' is the definition.
(synonyms)
'american is no smarter than anyone else' is the wordplay.
I cannot really see how this works, but
'american' could be 'a' (common abbreviation - e.g. in organisation names) and 'a' is present in the answer.
'is' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for leastwise that I've seen before include "in Hollywood at any rate" , "in any case" , "anyway" , "infrequently occurring" , "However (US)" .)