That reasoning doesn't really make sense. A flight from outside the US that is inbound could divert to a non-US airport that isn't impacted by whatever is going on, depending on where they are and what their fuel status is. A domestic flight doesn't have a non-US airport to divert to.
(Sure, a flight near the Canadian or Mexican border could in theory divert to a Canadian or Mexican airport, but it's unlikely many people on those flights have their passports with them.)
> (Sure, a flight near the Canadian or Mexican border could in theory divert to a Canadian or Mexican airport, but it's unlikely many people on those flights have their passports with them.)
There must be some procedures in place for this - I pretty regularly take domestic (Canadian) flights that pass over the US where I don't carry my passport.
A domestic US flight can still divert to Canada. There usually are special arrangements that allow people on a diverted flight to stay short-term while the situation is resolved, even if they don't have the required documents or visas.
Ah, my point was more that if the action being taken isn't "get planes on the ground _now_" and so the US airspace remains open for traffic already in the air, then it's unlikely they're trying to get international planes to either divert or return.