When lab rats do not know when pushing the feed bar might reward them (random reward, like a slot machine), they won't know when and where to fear an attack. Uneasiness will be a part of the American psyche.
The response would have to be swift and severe. This will be a tough decision for our President. Suppose the actual terrorists involved in that plot were hiding out in a remote place in an otherwise decent and peaceful country (the Philippines, say). Are we going to bomb the heck out of our friends?? It's not a nice scenario.
Some of you would say, take it to the centers of Islam -- blame all of Islam for not reining in their extremists. However, you can't blame innocents for being duped into donating money for what they thought was charity when it really went to terrorists, or being afraid of standing up to the terrorists for fear of deadly reprisal. That would be like killing all inner city residents who were there but "didn't see" the latest gangbang.
Deciding what the response would be and carrying it out would be a political career-ending move, no matter what the choice, though it would ensure reverence and history book chapters forever. It would take a leader with a simple ego who wants to make America safe for his great-grandchildren to make that call.
I suspect we might be occupying Teheran and Damascus in short order. Maybe with Russian help.