One obvious question Rosenbaum fails to ask is: why did the Cheney Administration promulgate NSPD-51 now, and why do we even need it? The obvious pat answer would be: because we now face a terrible, omnipresent Terrorist Threat. Anytime you open your sock drawer, a dirty bomb could go off, etc. But that is nonsense. We faced much greater danger during the brinksmanship period of the cold war, but there were no coup blue prints being filed then.
To unravel the mystery, it's important to first note that the American people don't need NSPD-51, and don't benefit from it. The USA has multiple layers of mostly robust and highly functional local government to keep order in a crisis. If everything inside the beltway were abruptly vaporized by space aliens, the American people would not suddenly run around like headless chickens and starving madmen, in desperate need of "continuity." In the short run, DC is largely unimportant to daily life.
Largely, I say, because there is one real issue of concern: simply the currency and financial system. After a disaster, will three dollars still buy milk? Will the banks open on Monday morning? Will Social Security checks arrive in the mail? Americans don't need the Pentagon to live, but we do need First Data Corp to process our credit card charges. Having not read all of NSPD-51, I am not sure if it addresses the currency and financial system, but anything beyond that is not done for the benefit of the people. There is some other purpose.
That other purpose is easy to divine by carrying forward the example mentioned above. What would happen by way of emergency if the contents of the beltway suddenly disappeared? Daily life at the local level would carry on until we cleaned up, built a new capital etc. What is the one thing that would suddenly be in trouble minus the beltway (or minus beltway power)? You guessed it -- the Iraq war. Vaporize DC and the Iraq war would be abruptly over.
The answer to the question why NSPD-51 now is: the assumption that we will be waging foreign wars on a permanent basis from now on. The real challenge for the beltway crowd is how to sustain foreign wars in the event of an emergency, considering that the people never supported these wars in the first place, or only did so under the influence of intense false propaganda. After a major disaster, the American people would look inward, and lose interest in foreign (Israeli proxy) wars being managed by the beltway elite. Even if the disaster were a terrorist attack, there would be plenty of critics who argue that America wouldn't be attacked if it weren't trying to occupy the whole Middle East. The challenge for the beltway crowd is: how do they marshal enough power to sustain unpopular foreign wars even at a time of domestic disaster? How do they silence critics and make sure that inconvenient democratic processes or simple disregard of central authority don't undermine the war effort? The answer is a blueprint for martial law, as we have seen.