Because Israel managed to pull of a wildly successful operation to capture the American politics by very aggressively promoting the notion that being in any way, shape, or form against anything Israel does is rabid anti-Semitism, and then using that as a cudgel (backed by a lot of money) to beat any candidate who might want to say something about it.

See also: https://en.wikipedia.org/wiki/AIPAC, which is an obvious foreign agent that's blatantly operating in violation of https://en.wikipedia.org/wiki/Foreign_Agents_Registration_Ac... for >70 years now.