This is true: the internet could easily be shut down, at least in the US, by the federal government, and hopefully not anyone else. All they would have to do is

This is true: the internet could easily be shut down, at least in the US, by the federal government, and hopefully not anyone else. All they would have to do is go to each ASN, find the BGP instance, and physical shut that box off, or order ISPs do to it themself. The ISPs could run, but without talking to each other, there is effectively no "internet". There are other things, like shutting off some exchange points/fiber optic network that would have a serious regional effect as well. It's all very possible to do.