> basic use & possession in this context

Try openly producing and selling. Multi-million dollar businesses operating in open plain view of the public and any federal agent. States legalize cannabis and the federal government in turn stops enforcing their laws against cannabis in those states, demonstrating that the states have de facto sovereignty to legalize drugs. They didn't just stop prosecution for "basic use" and possession, they no longer enforce their drug laws against growers and dealers either. They've essentially given up, for the time-being at least.

The fact that the same states are not also defying federal gun laws (with some interesting exceptions *cough* alaska *cough*) is another matter entirely. The federal government does seem to be more keen on exercising their sovereign powers when it comes to guns than with drugs.

I'm specifically referring to gun laws that pertain to "illegal drugs", so you can't really decouple the two like that. Not only the feds actively enforce these in all states, but even their forms that you have to fill explicitly state that cannabis is an illegal drug even if legalized in your state of residence. So, in effect, the states do not have full sovereignty even wrt drug legalization in all contexts.

The federal gov has no power to declare drugs illegal. It is not within their enumerated powers: Article 1 Section 8.

You can say they don’t have the power all you’d like, but after 50 years of them enforcing it, you’re not likely to convince a judge they can’t do what they do.