The obvious next step should probably be impeachment and removal from office. This seems to be the sort of situation was intended for. Elderly president goes completely off the rails one Friday and attempt to take out the global economy and trigger world war 3 for reasons that nobody can articulate. It is difficult to find a perspective where this war was reasonable, necessary, well advised, legal, moral or agreed to by any of the bodies that are supposed to decide whether the US military activates.

The only vague silver lining is that the situation is such a disastrous blunder that maybe future presidents will think a bit harder before sending the military in to the middle east. Assuming that Iran doesn't survive, get nukes and set up an impenetrable missile deterrence that renders the question moot. If the Republicans don't disassociate from Trump ASAP it looks like it is going to be much worse for them than Bush was and the way he established a good decade of right-wing cultural irrelevance. The safest path that will hold together with hindsight is walking away but I doubt they're nimble enough to manage that.