Wiping out an American city, much less the largest ones, requires either blast yields well beyond the capability of any terrorist organization, or numbers of nuclear weapons that would make the terrorist organization one of the largest nuclear powers on the planet. This is particularly true of major cities such as Atlanta, Houston, and LA, which are defined by their suburban sprawl. Size Matters The US and USSR encountered this problem early in the arms race. They were building larger and larger bombs in their show of force, but these became ever more impractical to deliver if ever called upon - to say nothing of the cost to maintain. They eventually realized that they could achieve the same level of destruction by detonating lots of small weapons in a tight pattern. ... The Aftermath It only takes minutes for panic to set in among the survivors. The 120 million people—more than one in three Americans—who live in the affected metropolitan areas are now desperately trying to get anywhere else but the cities they call home. Outside the targeted cities, panic sets in as news of the blasts floods the Internet and the surviving cable and television networks' broadcasts. People voluntarily evacuate other cities as rumors and fears of additional bombs spread. In Washington, DC, there are more pressing concerns. The bomb was detonated at 16th and K St, NW, just a few blocks due north of the White House. Whatever little of the mansion the 50psi overpressure did not destroy, the intense thermal radiation has ignited. The President and Vice President are almost certainly dead. At the other end of Pennsylvania Avenue, the Speaker of the House, second-in-line to the presidency, was in his office overlooking the National Mall. When the fireball rises over the ruins of downtown, he has no shielding from its full effect, suffering a mix of second and third degree burns on his exposed skin. Some loose papers in his office ignite, and wood surfaces scorch. When the blast wave hits the Capitol Building, it is a mere 2 psi overpressure – not enough to knock down the marble, but plenty to turn its blast-facing windows into projectiles. The moment the Speaker's security detail, who were sheltered in the halls of the Capitol, rush in to evacuate him, he is alive, but in critical condition. There is now a leadership crisis. More details via Gizmodo.
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