If someone dropped a nuke on New York City, what do you think would be the most important thing on the priority list. Would you focus first on:
First and foremost you find out who did it and nuke them. Failure to do so is an open invitation for a second bombing. Always plug the leak in the boat before you try to pump out the water.
I'm no fan of NYC, either. But if you don't nuke the perps three times over they'll hit nashville next.
First off, I would want to be briefed by experts on nuclear fallout and contamination on what a safe radius around ground zero would be and evacuate anyone within that perimeter. That would be the first and most important action. While this was happening, I would want to be in touch with military and domestic law enforcement officials to lockdown the area and assess any additional threats that may exist to the country and our allies. I would want a briefing on who our intelligence, assuming there is any, suspects is behind the attack. Five minutes after I received credible intelligence that satisfied any reasonable doubts I had about the people behind the attack, missiles and bombers would be in the air. I would not strike back with a nuclear attack. One is enough. I'm not a pacifist, and I'm not a war monger either. War should be the final course of action, but you had better believe that any strike against my country(especially if I was in charge, which is what I'm assuming is the perspective for this question) would be met with a heavier and immediate response. There would be no measured response, but neither would there be any political theatrics and fake threats like we saw from Bush about Iraq after 9/11. As the military options are being considered, I would want to be in contact with FEMA and the heads of all state relief agencies to coordinate a nationwide relief effort aimed at helping the victims and preventing as many additional casualties or sickness from the aftermath and the fallout. The National Guard of all nearby states would be mobilized to provide security. All law enforcement officers of any Federal, state, or local departments would be on high alert and on call. I would direct the Attorney General to make it his personal and sole mission to make sure anyone taking advantage of the situation either through theft and looting or price gouging would be met with the most severe legal ramifications imaginable. I would then want to make contact with our allies, both military and non-military, as well as convene an emergency session of the UN to which I would speak via videoconferencing so I could remain in whatever bunker, airplane, or building I am in which will likely have all the technology I need to maintain contact with those I need to be in contact with and monitor the situation. Visiting the area and putting up a public face will come later. I would not be asking the UN permission for any retaliatory measures, but instead trying to coordinate any efforts on their parts either to aid in the disaster in our country or deal with the international threat that had presented itself. I would be in contact with whomever I would need to be speaking to about securing clean uncontaminated water and food to be shipped to outlying areas around ground zero, where there would likely be a great deal of survivors in need of aid.
Find out who did it, or might have done it, or tried to do it, or could have known about it beforehand...and kill them all. Medina should also be incinerated.