Yes, but these are the major airports for international flights, where those coming from Europe/Asia/Africa are most likely to enter (they have to go through customs). If it's ISIS that's doing it, then it's a game changer and they'll send them into Mexico and run them across the border instead of trying to slip them in by air. Or, if they have enough volunteers, they could try both approaches.

Either way, it's too little, too late for the US.