This is probably the worst idea I've ever heard, it just reeks of power abuse. What next, should we give the president the right to shut down all libraries in the nation and to halt all book reading, just in case there is an information crisis? This is a horrible law, There is no way just shutting down the internet is going to somehow save the US. This isn't hollywood, people don't take 20 mins to upload a virus into our missile silos that we could somehow prevent in a death defying leap to save the world.
Even if there where some sort of real danger, by the time the president hears about it, it would be too late to act. Computers are freaking fast, our reaction time is nothing compared to a modern processor. (even a 10 year old processor)