With nearly 40 million people, the innovation powerhouse of Silicon Valley, and the sixth-largest economy in the world (larger than France’s, Italy’s, and India’s), California is a force to be reckoned with. And it’s got bones to pick with Washington, on issues from environmental protections and health care to immigration enforcement and drug policy. What are the legal and constitutional underpinnings of California’s challenges to the federal government, and what can we expect to come of these clashes?