Interstate commerce clause. It's been the reason for many the Congressional abuse, and it would be my go-to for any time I ask, "why can't the state(s) just tell the Feds to piss off?"
"Because in some infinitesimally small way, someone might lose money."
I don't personally smoke weed, but I'm still incredibly offended that the Supreme Court ruled that the feds can prevent you from growing your own personal supply because of the negligible impact it might have on interstate prices.
"Because in some infinitesimally small way, someone might lose money."