Actually - they can legalize it. Several states have imposed initiatives intending to legalize it completely. Wether the feds respect the state laws is another story to be addressed by the federal court system, eventually the supreme court will have to deal with this horrid distortion of the legal system.
The feds won't be able to get away with this much longer. IT is a blatant abuse of power, the constitution was created to keep the federal law from violating state law which it clearly has. What the feds have been doing to the dispensories in California is nothing short of THEFT.
The situation the feds are imposing in California is infuriating, I don't expect that the people will stand for it much longer.