Indeed. And it's doubtful he'd have to use troops and cut power lines; if it really was a observable national emergency, his request would be enough. People grant amazing deference to putative leaders in uncertain/dangerous times, and the people in private organizations who run various systems aren't antigovernment ideologues, idiots, or malicious foreign agents. It's only requests that are wildly unreasonable, open-ended, or based-on-secret-evidence that they'd resist. So there's no need to formalize this sort of Presidential power.