American institution enthralled by PM providing chief support (8)
I believe the answer is:
mainstay
'chief support' is the definition.
(I've seen this before)
'american institution enthralled by pm' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'institution' becomes 'inst' (I can't explain this - if you can you should give a lot more credence to this answer).
'enthralled by' indicates putting letters inside ('enthral' can mean 'capture').
'pm' becomes 'May' (former UK prime minister Theresa May).
'a'+'inst'='ainst'
'ainst' placed within 'may' is 'MAINSTAY'.
'providing' is the link.
Can you help me to learn more?
(Other definitions for mainstay that I've seen before include "chief supporter" , "Linchpin, principle support" , "Strong cable that secures a mast, chief support generally" , "Strongest support" , "Strong cable to secure mast, chief support" .)