If a Nuclear bomb were dropped....

[Excited Penguin]

The United States would not be the only ones to react.  The entire world would react.  A nuclear bomb going off in a major city?  That's not something any major country in the world will sit idly by and tolerate.  I imagine that most major countries would quickly declare their own war on terror, and probably against terrorist backers as well.  There would also be a large scale relief effort.  

If a country was found to have supplied the bomb to terrorists, then that country would probably face nuclear retaliation.

The NSA surveillance would increase, and we'd probably see a Trump-Esque response to immigration.  Our rights would be trampled on in the name of security.

I agree with everything except the dark tone in which you cast the last sentence. It would be an unfortunate thing, but certainly necessary. Both better immigration screening and surveillance, that is.