President's affirmation in code (7)
I believe the answer is:
bushido
'code' is the definition.
(I have seen 'honourable code' mean 'bushido' so perhaps 'code' could also mean 'bushido')
'president's affirmation' is the wordplay.
'president' becomes 'bush' (George H W Bush or George W Bush).
'affirmation' becomes 'ido' (I can't explain this - if you can you should give a lot more credence to this answer).
'bush'+'ido'='BUSHIDO'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for bushido that I've seen before include "chivalric code" , "code out east" , "honourable code" , "Strict ethical code of Japanese samurai" , "Feudal code of the Samurai" .)