Herman Cain has been gaining much traction with his 9-9-9 Plan, a bold proposal to replace our dysfunctional tax code with what could be a simpler, less invasive, and more economically stimulative alternative. While I don't agree with the full spectrum of Mr. Cain's policy choices, I applaud his courage on the tax front. Judging by his rising poll numbers, this appreciation is widely shared. However, the plan has deep flaws, the most glaring of which is its creation of a hidden payroll tax which represents a fourth “nine.†This serious pitfall has been unmentioned by Mr. Cain and overlooked...