Not only it should be, it is already illegal, for a long time, as foreign aid to Israel violates two amendments of the 1961 Foreign Aid Act, which ban aid to clandestine nuclear powers. It's broadly know Israel has nuclear weapons, and politicians there keep threatening Gaza with a nuclear holocaust [1], but the US government keeps unlawfully bankrolling them.

[1] https://www.middleeastmonitor.com/20240124-israel-minister-r...