I think Israel, Ukraine, and Taiwan are all similar in this sense - they have chosen to be hostile to a larger neighbor (or, in the case of Israel, have chosen to locate AMONG a larger neighbor known to be hostile) in teh false belief that, somehow, the US will “have their back” in the absence of a formal treaty.
This is, in all these cases, false. If the three states involved believed it to be false, their policies might be different.
Bit of a quibble, while the USA is very much the most important partner of Israel today (both militarily, via clandestine services, and technological innovation) (and vice-versa — we are described as a “unsinkable aircraft carrier and beachhead”, with more than a million person military), that was no always the case.
The USA was not a particularly great ally at the start and your State Department downright hostile to the establishment of of Israel as a sovereign nation. We (sadly) had to turn to the Soviet Union for help -— part of why we are still rot through with stupid communists.