Act of War against Saudi Arabia, sure.
But why do I care?
I’ll say it again. Saudi Arabia ought to respond militarily. If we haven’t already sold them enough weapons to respond proportionately (or maybe twice as hard would be better) we should sell them more.
What I don’t know if they yet have the weapons they paid for. That might make a big difference on how to respond.
My impression is the UN Security Council will be convened before any action is taken. It could mean pressuring other nations (like France) to impose more sanctions.