International negotiations struggle to keep pace with global problems like climate change. To fill this gap, local governments increasingly take matters into their own hands. For example, to promote the benefits of clean energy, a local government might give subsidies to renewable energy companies. Since 2001, California has given $2 billion in such subsidies, while states ranging from Minnesota to Kansas and Mississippi have doled out hundreds of millions of dollars each. Cities, such as Austin and Los Angeles, have also gotten into the act, contributing millions to renewable energy firms. To build support for these measures, the local government might condition the subsidy on the recipient’s use of components manufactured in the locality....