There's no legal mechanism for the vast majority of what the president has done.

Often it happens anyway, along with some protests, some resignations and maybe an eventual court case reversal months or years later.

There are ways for the government to do that sort of thing on an emergency basis, and it would take quite some time to make it's way through the courts. There are precedents from nuclear weapons technology and cryptography. I don't think it'll hold up or be particularly effective because the horse has left the barn already, but they could probably slow things down if they really wanted to.

Of course there is. Fully automatic weapons are banned. Certain chemicals and biologics are banned. Certain hacking tools are banned (DMCA):

> The “tools” prohibitions, set out in sections 1201(a)(2) and 1201(b), outlaw the manufacturing, sale, distribution, or trafficking of tools and technologies that make circumvention possible. These provisions ban both technologies that defeat access controls, and also technologies that defeat use restrictions imposed by copyright owners, such as copy controls. These provisions prohibit the distribution of software that was designed to defeat CD copy-protection technologies, for example.

https://www.eff.org/pages/unintended-consequences-fifteen-ye...

I'm sure they will find something when it really starts to bother them personally.