ICANN is decentralized and has a lot of in-built security that prevents one site from infiltrating or poisoning the rest of the overall system. That’s why no governments have tried to fuck with it. Not only would it not work, but it would potentially become an international incident. But ICANN is really only the keeper of TLDs anymore, they don’t run any other base infrastructure of the overarching internet. You don’t need domain names to make IP networks talk to each other (ie: darkweb).

The only thing Trump could try and do is push ISPs to conform to laws Congress passes that influences the way network traffic is run (filtering, blocking…etc), which is what China has done with their Great Firewall shit. This would not end well for a number of reasons, and just isn’t likely or feasible to happen in the US.