When Colorado and Washington legalized marijuana by decisive margins in initiatives last November, they set up not just one but two conflicts. The first, of course, is about drug policy. No less important, albeit less widely noticed, is a conflict about power. To what extent can and should the states act independently of the federal government on an issue with national ramifications? The choices that Colorado and both Washingtons make over the coming months are likely to affect the course not only of drug policy but of state-federal relations for years to come.