For a midterm report card on the economy under President Trump, take a look at two recent government reports. The Commerce Department reported Thursday that real gross domestic product grew by 3.1% from the fourth quarter of 2017 to the fourth quarter of 2018—the largest rise in 13 years. And last month the Congressional Budget Office reported that even if the current surge in economic growth isn’t sustained, the revenue residual from our current strong growth rate will pay for some 80% of the projected cost of the 2017 tax reform. While these reports reflect only the initial impact of the tax cuts and the deregulatory...