I agree it’s the Congress who has that power. One thing I’ve wondered- what if nukes are airborne and about to hit us. Should we gather Congress together to declare war? I think it might be a bit difficult, unless Congress has prepared for such possiblities in advance.
Good question. Does the executive have the autonomously authority to defend the US against attack? Defending the US against enemies foreign and domestic is part of the oath of office, but I am not sure where the authority for immediate, autonomous action would come form.