I do not know the specifics, but some kind of a contract - “provide for the defense against attack” and such.
Ofc you could argue that genocide could invalidate that contract, though much like the outright war crimes happening in Ukraine, you would have to prove that, to a governing body (and again, doesn’t Israel have a veto power there?). Also Biden then loses any negotiation leverage he had to employ the carrot rather than the stick.
Also, there is whatever reason (cough oil cough) that we made the contract in the first place. If gas prices suddenly spike through the roof, Americans will complain bitterly and LOUDLY, and place ALL of the blame onto Biden, with NONE of it going to Israel.
Also, none of this matters really, b/c the job of President entails enforcing the contracts, not making up new ones - that is the job of Congress, who despite the fact that the 2024 federal budget started last October (look it up) STILL has not managed to pass the budget for THIS YEAR, 2024. We are nearly halfway through the ENTIRE YEAR - five months and 2 & 1/2 weeks behind us already - and despite ousting McCarthy and replacing him with Johnson, Congress is still gridlocked. Especially on this matter. And on Ukraine. And on the border. And on literally everything else.
People forget: but it is the job of Congress, not the President, to make funding decisions, like what monies go to what other country - otherwise he is bound to simply enforce whatever contracts were PREVIOUSLY signed, and there is only so much he can do to change that without their approval. This is what democracy looks like: to enforce the will of the people, who unfortunately are a divided nation right now, particularly on this matter where half the nation wants to send aid to Hamas, while the other half wants to send further aid (as in MOAR weapons) instead to Israel.