According to Stuff, the US – or at least, some its senators – consider the Internet a national (i.e. American) asset and believe that the US President should be able to shut it down. Gosh.
By the same logic, the UK owns the international postage system. The Queen should be empowered to shut that down at will.
Seriously, it’s hard to doubt that the US could completely crash the Net if it chose. But it would be an act of infamy that would damage the economies of the rest of the world far worse than the banking crisis. How much more bad press do they need?