The problem is perhaps clearer now, at least to Democrats, because Trump has done more than any other US president in history to make Congress irrelevant and govern without regard to law. But the problem was already in place before Trump. The legality of a presidentially ordered attack cannot depend on whether the Iranian regime collapses, as Gaddafi’s did, or manages to persist and fight an extended war against the US, as Iran’s might. Nor can it rest on the supposed invulnerability of US forces, who are certainly in harm’s way now. War must be understood to mean war. Hostilities must be understood to mean hostilities.