When Steven Chu, a Nobel physicist who had lately devoted his career to climate change and clean-energy research, was nominated by President Obama for Energy secretary in December 2008, it seemed like a perfect match. Until then, the Energy Department had actually played very little role in energy policy. Despite its name, the agency's chief mandate is to guard the nation's nuclear arsenal, and to clean up Cold War-era defense nuclear waste. In most years, about two-thirds of its budget goes to nuclear weapons and waste cleanup, while roughly 10 percent to 15 percent goes to energy research. The idea...