Trump bears some responsibility for threats like this. Several people, including Republicans, and many of our top Generals, and constitutional lawyers have told Trump that (1) he is taking an approach that creates constitutional issues by among other things discriminating by religion., and (2) he should follow Obama's previous orders based on persons who might be terrorists and not countries--believe it or not, there are more than six countries from which terrorists can come. Obama looked at where people went (like did they visit regions of Iraq which are the site of terrorist training centers) regardless of whether they were citizens of Syria or Egypt or Canada). Trump can tighten up the language or he can lower Obama's limits on numbers of immigrants, but keep the form of the order.