Do you think threats and missiles from an adversary are insufficient cause for war?

Yes. They didn't attack the US. We attacked them with no casus belli. Operation Epstein Fuckup.

Article 51 recognizes states' rights to individual or collective self-defense. Israel has a plausible self-defense claim based on the Iranian regime's proxy attacks against it, and its explicit mission of destroying it. If we accept that premise, then by extension Israel's allies also have a right to act in its defense.

There could also be separate arguments that the Iranian plot to assassinate Trump gives the US casus belli.

[delayed]

How is that relevant? There’s no exception to self defense for countries we once meddled with.