The Republican framework for tax reform is taking considerable heat. Former Treasury Secretary Lawrence Summers calls it an “atrocity.” Economics Nobel Laureate Paul Krugman describes it as “ten big lies.” These strong reactions rest in large part on a preliminary analysis of the plan from the Tax Policy Center. It claims that the tax plan won’t expand America’s economy or its tax base but will produce massive deficits. This pessimistic view does not reflect the best economic analysis.

Start on the business side. By our estimate,...