Of the 17 states that have passed medical marijuana laws, only one — Montana — has experienced a serious legislative effort to repeal the law. How could this have happened, and what can advocates in other states learn from Montana’s experiences? Fortunately for those of us who work to pass — and improve — medical marijuana laws, an excellent new documentary film provides a unique and insightful view of Montana’s 2011 repeal effort. Code of the West, directed and produced by Rebecca Richman Cohen,…