I've heard a little bit about this bill, particularly about the "President can shut down the internet" part. Can anyone explain how shutting down the internet c

I've heard a little bit about this bill, particularly about the "President can shut down the internet" part. Can anyone explain how shutting down the internet could help national security? I was under the impression that a cyber attack's point was to do exactly that. It seems like, I don't know, poisoning our water supply so that terrorists can't do it first.