When Ronald Reagan won the presidency, in 1980, it was a victory long in the making. For almost half a century, conservatives had plotted ways to cut taxes and undo workers’ rights. Their playbook for political influence went something like this: create a think tank, publish reputable reports, build relationships with journalists and politicians, and disseminate free-market ideas to the public, creating a new common sense. Today, the art of political influence is rather different. Think...