Right - and also it is important for them to see that the only reaction from us is us getting tougher, not weaker and in 'fear' of them.
I am not suggesting weakness. To the contrary. A tactical punt is done to survive to pummel them later. But if I worked in NYC, I'd take tomorrow off if that was possible. I'd go there if it wasn't. And if I was the mayor, I'd figure that a missed day's work by City admins isn't going to break the US economy.
Credible or not, they have given us no reason to fear their words in recent times. I do believe we will be attacked again shortly, but there is no way to tell if this is the time. I am sure the action taken has already gone a long way towards postponing the event, at the very least.