Malign American's behind trouble (6)

I believe the answer is:

assail

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'malign american's behind trouble' is the definition.
I can't tell whether this defines the answer.

'behind trouble' is the wordplay.
'behind' becomes 'ass' (both can mean one's back side).
'trouble' becomes 'ail' (synonyms).
'ass'+'ail'='ASSAIL'

Can you help me to learn more?

(Other definitions for assail that I've seen before include "Maybe mug" , "Make violent attack on" , "Aggressively attack" , "Attack violently and persistently" , "Criticize" .)

I've seen this clue in The Independent.

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