If anybody is wondering the background of the DEA's relationship to decisions made on drug policy, and how that relates to the DOJ, drug enforcement, federal laws, state laws, and treaties... I can explain a bit. Also a great summary of current reasoning is here: https://www.federalregister.gov/documents/2016/08/12/2016-17960/denial-of-petition-to-initiate-proceedings-to-reschedule-marijuana
The most simple thing to understand is the constitution gives authority to the federal government to basically exist - this is where the federal governemnt is granted its power.
...In the UK I believe the crown gives authority to parliament; another example the Holy See gives the Pope authority. Its an important distinction to understand when figuring out who has the authority to do what. Back to the USA and marijuana...
The Supremacy Clause is the mechanism by which this authority is derived: https://en.wikipedia.org/wiki/Supremacy_Clause
This also allows the Federal gov to enter Treaties, which supersede Federal law.
At the bottom of the power structure, as given authority by the constitution, are state rights and authority.
The Treaty that governs USA drug law is outlined in three documents called: The International Drug Control Conventions. They can be viewed here: https://www.unodc.org/documents/commissions/CND/Int_Drug_Control_Conventions/Ebook/The_International_Drug_Control_Conventions_E.pdf
These treaties allow the USA to at best schedule marijuana as Schedule II drug. The USA, and any other nation, is allowed stronger scheduling as they see fit - the USA saw fit to schedule it a Schedule I.
We cannot change our federal law to allow full federal recreational marijuana under these Treaties and conventions. Its not allowed.
For states who have allowed recreational could argue that since their states, and marijuana users in those states, are small compared to the overall USA population, that recreational marijuana could allowed as it would not be a federal mandated practice.
Also I believe there is no punishment for violations. It seems to be beyond the authority given. So by that measure only a state could punish an individual.
Medical Marijuana would be allowed as long as it was not open to abuse (doctor oversight), and has accepted health benefits (it does) - then it could stay a Schedule I without congress needing to make it a Schedule II.
Or the USA could leave, or amend, the Treaties.
The state has no claim to make laws in violation of federal law and signed treaties. The state is not given authority by any mechanism to allow this - even by a state supreme court decision, or vote of the people in that state. The authority rests on the Treaties to divvy out to countries.