I think this issue encapsulates much of what we'll be facing - an issue long thought settled (marijuana has been a Schedule 1 drug for decades) is being reopened and fought against from the ground up, the public opinion on the illegality of pot has shifted dramatically and the governing structures in place are lagging significantly. While legalization has proceeded on a state-by-state basis, it is still illegal at the federal level.
This dynamic between the state-level approach to ending marijuana prohibition is fascinating and could inform the way other expressions of negative mood might get implemented. In short, having the states legalize this substance while still keeping it illegal under federal law - and letting the states go forward in this manner - is straight-up old school Nullification. Now, legally there is actually a bit more gray area as the states are not technically voiding Federal law, but the next step to replaying the Nullification Crisis isn't a big one and certainly not inconceivable should the next economic crisis prompt Federal laws which dramatically and negatively affect key states such as California, Texas, or Florida.
This tactic - of using state laws to neuter or otherwise render hard to enforce Federal laws - is also being tried with gun rights issues.
Makes you really wonder what else we might see in this arena. If cyber security becomes the next big bogeyman and the US moves in the direction of the UK as it attempts to ban all encryption that can't be compromised by the government, does California set up its own laws in defiance of a federal ban? What other areas do you see the states setting up in opposition to the Feds?