Fighters at 26 airbases across the United States are in standby alert to protect the 103 nuclear reactors in the country and to react immediately if any aircraft begin moving in an unsual manner or divert from course.
Law enforcement agencies and the armed services within the continental US are at an unprecedented level of alert.
Reactor sites are being considered "part of the homeland defense," according to Richard Meserve, head of the Nuclear Regulatory Commission.
Opinion: If there is going to be another wave of attacks, it is most likely to take place in response to US military action abroad.
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