Why doesn't the U.S. simply ban all Chinese products that have an internet-connected computer in them? That would solve almost all security problems in one strike and force Chinese manufacturers to communicate via Bluetooth and update software through USB sticks or memory cards.
The apps communicating with said devices through Bluetooth obviously can't connect to the internet either otherwise there'd still be an avenue for subversion.
Just banning one Chinese product category at a time willy nilly doesn't help as there are a zillion other product categories of Chinese stuff with internet connections. From toys (with camera's in them), to refrigerators, power converters, microwaves, televisions to smartphones.
Going one at a time, in small apparently myopic focus is how a politician shakes the lobbyist money tree. "You could be next!"
Probably why you couldn't ban all at once...there'd be not much left.
Removing an internet connection doesn't really solve much when you're talking about autonomous AI-driven robots with vision and hearing. It's a whole different category to toys, refrigerators, etc. My refrigerator isn't going to suddenly pick up a weapon and start attacking things on command. Nor does it have an easy way to receive instructions through side channels. I'm not saying I agree with Trump's policy - but removing internet isn't a solution either.
While that seems helpful it would not be enough. Consider this as a counter example.
Why does Ross, the largest Friend, not simply eat the other five?
There's a box being sold called "SuperBox". It claims to be able to stream any movie/video. The claim is "just pay $300 and you won't need to subscribe to any streaming service anymore." However, part of what it does is hacks your home network and tries to take over every thing on that network. And it sends this all back to China. The vast majority of people buying & installing these are just ordinary people but some will be executives, or people working for the feds. Did they bring their work laptop home and plug it in to their network? So it can get attacked outside the office firewall? Remember how stuxnet was spread?
This is a podcast about it: https://darknetdiaries.com/episode/172/