Big US donor's attendance restricted by what he calls checks (4,5)

'what he calls checks' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'big us donor's attendance restricted' is the wordplay.
'big us donor' becomes 'bills' (I can't justify this - if you can you should believe this answer much more).
'attendance' becomes 'gate' (I've seen this in another clue).
'restricted' indicates putting letters inside.
'bills' placed around 'gate' is 'BILL GATES'.

'by' acts as a link.

Can you help me to learn more?