Forces on the Mexican or Canadian border. Forces on either seabord. Forces on the border of Alaska. Forces inbound to Hawaii. Missiles fired from any nation in an attempt to attack the U.S.
That about covers it. Any of those is an act of war and merit a swift and deadly response.
It's easy to figure out if you just imagine what course of action you are allowed to take when you are yourself threatened. When are you as an individual allowed to use deadly force?
I think most Americans would find your thresholds for justifying military intervention too high. That was the reason for asking you who would decide when to launch the military. In your scenarios, you have waited too long to intervene. There may be early methods of intervention that would be less risky for everyone involved than waiting to be attacked. I also don't think that drawing an analogy to personal protection is legitimate. We have a body of laws that have developed around self-defense based on our own history and jurisprudence. Not everyone in the world will agree to the standards we would hold overselves to. I don't believe that personal rights are the same as international rights and I don't think our ideas on freedom translate very well to nations that don't concur with our ideals.
For discussion purposes, however, you do have an advantage in arguing that position. It is basically an untestable hypothesis since no one with those views will ever be elected to a position to implement them. Therefore, it is easy to argue about it being an idealistic position without ever running the risk of being disproven.