Jeff Bell was a reform conservative before it was cool. He’s spent his career arguing with a risk-averse Republican establishment. He pushed Ronald Reagan to embrace the supply-side doctrine of tax cuts before deficit reduction. He spent the 1990s warning the GOP that its tax policy favored investment capital over human capital, corporate interests over working families. He designed a family-friendly flat tax that reduced payroll taxes, increased the child tax credit, taxed capital gains and regular income at the same rate, and ended business expensing. Payroll tax relief and a generous child tax credit are elements of today’s reform...