American insults upset Russian legislature (4)
I believe the answer is:
duma
'russian legislature' is the definition.
(I've seen this in another clue)
'american insults upset' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'insults' becomes 'mud' (I can't justify this - if you can you should give a lot more credence to this answer).
'upset' is a reversal indicator.
'a'+'mud'='amud'
'amud' written backwards gives 'DUMA'.
Can you help me to learn more?
(Other definitions for duma that I've seen before include "Russian state assembly" , "Russian elected parliament" , "Russian legislative assembly" , "council" .)