If the Internet goes off, it means most of the US will be pissed off at him. Cellphones would be basically useless.
His followers wouldn't be able to access their favorite propaganda and conspiracy theories, either, so maybe they'd sober up a bit. Either way, it would not be good for him.
I mean, he can't. Even if he claims to have the executive power, even if he found a bunch of lackeys willing to try to do it for him, he can't do it. Whatever he did would be unenforceable. You can't just turn off the Internet. That's literally the reason we invented it in the first place, it's a communication network resilient against nuclear strikes and war and bad-faith governance all at once.
He could probably make it very hard to use, given a lot of time, but he'd be eaten alive by the angry populace long before it ever reached that point.
You wouldn't need an ISP to have servers communicate, if push comes to shove. So maybe "effectively off" as we know it, but damn near impossible to stop communication if people need it
I mean, off for whom? There's people who think facebook IS the internet and will be forced to go outside if they can't read their racist memes today. For critical comms, you'd have to shut off way more than 3 or 4 big companies to make a dent. For sensitive, high-bandwidth applications that involve a lot of people being online at once, you would need to hit fewer before the damage is noticeable.
I agree that the internet is far more than facebook. But if you're blocked at the edge of the network by your ISP, there's really not much you can do. You'll have access to nothing, Facebook or otherwise. Not even something low bandwidth.
If At&t, Comcast, Charter, Verizon, and T-Mobile suddenly stopped providing service to all their customers, then essentially no-one would be able to use anything on the internet at all. Even if the backbone itself (which I believe is largely owned by those same companies, but not sure) and some large datacenters that are their own isps were able to keep talking to each other, anything business or user facing would stop.
Some people who run their own mesh networks might be able to stay in contact (and people would try and start some local ones as this disaster unfolds), but that's so few people.
But we still haven't established why. It makes no sense that companies that only make money providing a service would stop providing the service. I wouldn't even be able to pay my ISP because that happens over the Internet.
I was assuming this was the government ordering the companies to. They have no incentive to do so on their own. But I believe there was a bill (which thankfully didn't pass) that would have given the president the power to essentially order the internet turned off.