If there is credible evidence or intel. that suggests a small nuclear device is going to be used against the US populace, the US already knows the few countries that have this technology and who gave it to the terrorist agents. Therefore the US should then through diplomatic channels threaten a full nuclear retaliatory strike upon the capital city of any or actually all of these select few nations if there is a nuclear attack against the United States. No questions asked. Kennedy, Cuban missile crisis. They must be forced to blink. If they know their imminent evaporation is in the works, they will work through their overseas communication network to alert their agents to stand down.
At about 2 in the morning (Eastern time), Fox News said that new information had just been received from the government, saying that the current emergency is very serious. They (the gov't) said that we have not seen such a serious threat since the Cuban missile crisis. They said that the most critical period would be within the next 72 hours.