This is a movement that has been growing stronger and stronger. Not only over the marijuana laws on state levels, but also regarding the imposition of Obamacare on states.
Nullification is getting to be more commonly used from criminal courts, to state courts, to federal courts.
Cannabis prohibition is unconstitutional. For alcohol prohibition there was a constitutional amendment needed to validate alcohol prohibition, and a constitutional amendment to repeal alcohol prohibition.
The same is needed for cannabis prohibition, yet there is no constitutional amendment regarding cannabis (for or against).
I wrote more about this here;