Just a thought: Trump DOES have the power to pardon people of federal crimes. How about pardoning all users of medical marijuana for the still very real federal crimes of possessing and growing their own. That way the DOJ can concentrate on real crimes and stop threatening a bunch of cancer and AIDS patients with prison.
It wouldn't protect them in states that still forbid it, but in 29 states, Guam, and Puerto Rico they would be safe. That is comfortably more than half the states in the union.
(Almost every state has added some sort of law allowing the use of medical marijuana. 29 is only the states that have effective laws. The others have some problem or another with their laws, like legal to use it but no legal way to get it.)