Federal regulation has been growing mightily since the early 1970s, powered by statutes that delegate Congress’s lawmaking authority to mission-driven executive agencies. Beginning in 2008, the executive state achieved autonomy. The Bush administration during the financial crisis, and the Obama administration in normal times, decreed major policies on their own, without congressional authorization and sometimes even in defiance of statutory law.

President Trump might have been expected to continue the trend. As a candidate,...