Experts caution that the most threatening scenario for cataclysmic nuclear war is an accidental nuclear launch from Russia due to their deteriorating early warning system.

While the United States struggles to rein in Iran's nuclear ambitions, a more frightening nightmare is simmering right now in Pakistan, where a weak but nuclear-armed government is being buffeted by radical Islamic influences, terrorism and several bloody insurgencies.

Seven years after al-Qaida took down New York's World Trade Center towers and struck the Pentagon itself, the United States does not have a coherent strategy to deter another attack, according to senior U.S. officials and analysts outside government.