Amid the debate over tweets and tax reform, perhaps the most significant change brought by the first year of the Trump Presidency has been overlooked: reining in and rolling back the regulatory state at a pace faster than even Ronald Reagan. This is a major reason for the acceleration of animal spirits and faster economic growth in the past year.

A rules rollback is harder than it sounds because the inertial tendency of bureaucracies is to expand, and the modern administrative state has expanded almost inexorably under presidents...