The US has an unfortunate record of waves of xenophobic nativism, odd for a country that once prided itself as a haven for refugees (Give me,your tired, your poor your weak, your huddled masses yearning to breathe free...) But more than in most cases, this is precisely the reaction the Islamic State hopes to provoke. It considers Muslims living in the West as a danger, and seeks to provoke anti-Islamic sentiment in the West to increase the number of potentially alienated young recruits.
Remember ISIS' preoccupation with Dabiq, an apocalyptic end-times battle mentioned in a hadith attributed to the Prophet. They actually want to provoke Armageddon. Let's not help them along.
Demagoguing the refugee crisis for political gain is not just sleazy; it's dangerous. Creating suspicions about your neighbors can lead to the worst kinds of fear, fear of an enemy that may barely exist. The internment of Japanese-Americans in World War II (most of them citizens) has actually been cited by some of the worst sort of politicians as a model.
What is the purpose of terror? By definition, it's to terrorize, to incite fear. Within days of the carnage in Paris all it took was a warning to evacuate the stadium in Hannover. Of course one should take precautions, but if all it takes is a phone call to evacuate a stadium, why should ISIS spend money making bombs. They've created terror with little effort.
An ISIS video that shows a man with an explosive device interspersed with stock footage of New York is getting a lot of attention, but it could have been made anywhere and the NYC scenes spliced in. Of course New York should ramp up security, and it can never forget 9/11, but it shouldn't cower in fear. A better response might be Rick's dialogue with the Nazis in Casablanca:
Major Strasser: Are you one of those people who cannot imagine the Germans in their beloved Paris?Don't give them what they want.The best way to combat them on the ground is something that can be debated, but action should not be undertaken without clearly defined objectives and the realistic means to achieve them. That's basic Clausewitz.
Rick: It's not particularly my beloved Paris.
Heinz: Can you imagine us in London?
Rick: When you get there, ask me!
Captain Renault: Hmmh! Diplomatist!
Major Strasser: How about New York?
Rick: Well there are certain sections of New York, Major, that I wouldn't advise you to try to invade.