On all matters relating to Israel and the Middle East in general, AIPAC writes the legislation (or letters, resolutions, etc) which are then handed over to legislators to drop in the hopper, gather cosponsors, and get it passed or sent. Not only that, the ideas for these initiatives come out of AIPAC rather than (as is usually the case with lobbies) starting with the Member of Congress who then asks the lobby for help with drafting. AIPAC does it all, from soup to nuts.
I know this because back in my days working as a Congressional aide, I participated in that process. Mea culpa!
I was working for Congresswoman Nita Lowey, a member of the House Appropriations Committee’s Subcommittee on Foreign Operations. Those are the committees that ostensibly produce the foreign aid bill, including the $3.5 billion Israel aid package.