SCOTUS may get involved:
The U.S. Supreme Court may be nearing a decision on whether to hear a case brought against Colorado by two neighboring states over marijuana legalization.
Supreme Court justices were scheduled to meet privately Friday to discuss the case, which was filed in 2014 by the attorneys general in Nebraska and Oklahoma.
Nebraska and Oklahoma argue that pot flowing out of Colorado is not only illegal under federal law but presents an undue burden to them. Colorado argues that their legalization doesn't affect the fed's ability to criminalize the weed, and the Choom gang currently in orifice has urged SCOTUS not to take the case. They may be disinclined to do so anyway, because it's going to be a biggie and with the death of Justice Scalia, they're down a member. So they may choose to punt for the time being.
Under the Supremacy Clause in the U.S. Constitution, federal law "trumps" state law when the two are in direct conflict.