Sclerotic growth is America’s overriding economic problem. From 1950 to 2000, the U.S. economy grew at an average rate of 3.5% annually. Since 2000, it has grown at half that rate—1.76%. Even in the years since the bottom of the great recession in 2009, which should have been a time of fast catch-up growth, the economy has only grown at 2%. Last week’s 0.5% GDP report is merely the latest Groundhog Day repetition of dashed hopes.

The differences in these small percentages might seem minor, but over time they have big consequences....