Well, it's a bit unclear EXACTLY what would happen, but I'm guessing a little like this.
To start, the first thing americans want to hear is what ACTION the gov is taking, both to retaliate, and to protect. My guess is our first move is to pull troops in from stationary positions around the world, and seal this country off. We then get concentration camps set up, and the army goes city to city rounding up ALL middle easterners, and administrating truth serums to see who is a good guy, who a bad guy. This of course is when the liberal nutjobs come out of nowhere and start screaming that this is a violation of their human rights etc, at which point the gov will gladly throw them into camps as well. This will all happen very quickly, within 60 days, and somewhere along the line you will see total martial law throughout the country, ID tags, can't be out past 9pm etc. The gov will naturally not be able to exactly determine who nuked us, but will come up with a theory on what country helped these guys, and they get bombed to fuck to kingdom cum, probably with MOABs, not nukes. I doubt we will use nukes, they are more or less our defense against an invasion from china or russia or something. When we have totally interrogated the arab population in this country, I think then we will mount some kind of large scale invasion in the middle east. Think millions of US troops. We will be back to WW2, everything will be rationed, and most able bodied men will be overseas. We will (FINALLY!) have a large electric fence between us and that shithole mexico, and probably one with canada as well. You will not be able to go in or out of america without being practically strip searched. This will of course kill drug trafficking, at least for a little while, and eventually the gov will regain lost drug war tax revenues through military spending. Our conquest of the middle east will last 10 years at least, and in the end, we will simply have accomplished a greater united states. Now this would all happen HOPEFULLY, my other thought is that when the nuke goes off, our sissy goevernment runs around protecting all the arabs in this country, and are totally preoccupied with it. I think not till the second city gets nuked will they do anything, but let's be optomistic.