It seems the states won that one, for whatever reason.
so states would argue that since pot is only legalized within their borders, and isn't (legally) sold across state lines, the CSA doesn't apply.
the Federal government would disagree, and would probably win in a fight citing Wickard v. Filburne or that machine gun case, but they couldn't force states to actually enforce their drug laws - it'd be a battle of attrition with the DEA, and it'd piss the states off.
honestly, I think they decided it wasn't worth the fight since pot is pretty popular, so they let sleeping dogs lie.
They did win that, see Gonzales v. Raich.
Congress used the power of the purse to forbid the Federal Government spending any money to prosecute those in states that had made medical pot legal.
>Congress included a provision in the 2015 spending bill prohibiting the DOJ from using any funds to prevent states that have legalized the use, distribution, possession, or cultivation of medical marijuana from implementing these laws.
In doing so, Congress was using the “power of the purse” as a check on executive power, one of its most important constitutional prerogatives. As James Madison wrote in the Federalist Papers, this power “may, in fact, be regarded as the most complete and effectual weapon with which any constitution can arm the immediate representatives of the people, for obtaining a redress of every grievance, and for carrying into effect every just and salutary measure.”
https://slate.com/news-and-politics/2016/04/obamas-medical-m...
Congress has renewed that provision every year since, and made it clear to the Trump administration that they would extend the ban to include states that had passed full legalization instead of just medical marijuana, if forced to do so.
Both the Constitution and the 10th Amendment make it pretty clear that the Federal government has no business in these area.
This and the Commerce Clause "loophole" can hardly be used to mingle in private state business as long as the firearms don't cross state line.
imagine if states pulled this tactic during integration..