>For instance when Iran gets the nuclear bomb and threaten Israel with it ?

I don't know if this was your intention, but it's exceedingly likely that the US would side with Israel in all circumstances if Iran threatened Israel with a nuclear weapon, no matter who is president. In fact, the threat of Iran attacking Israel was one of the key reasons† Biden refused to unilaterally stop all arms shipments to Israel.

† Source: War by Bob Woodward.

Given that Trump's foreign policy is quite alien compared to his predecessors, I don't know how valuable looking to the past is for this sort of thing. A new president, of any political bent, may follow the example and make further breaks with the past.

I agree for the most part, his foreign policy is very alien compared to Biden or any other "normal" president. When it comes to Iran and supporting Israel, though, I think he's still pretty hawkish and predictable for a Republican president (or as predictable as Trump can be). Remember during his first presidency, he withdrew from the Iran nuclear deal, then he imposed a bunch of tight sanctions on Iran while reinforcing ties with Israel and recognizing Jerusalem as its capital.

Part of his hawkishness toward Iran comes from the kinds of national security advisers he keeps (typically all hawkish on Iran themselves, with some exceptions like General Mark Milley), and part of it comes from his admiration for "strongman" leaders like Bibi.