Herman Cain has gotten a lot of attention for his 9-9-9 tax plan, Governor Rick Perry recently unveiled his own flat tax proposal, and there have been numerous presidential candidates who have made a flat tax plan the basis of their campaigns. Joseph J. Thorndike is the director of the Tax History Project at Tax Analysts and a contributing editor for Tax Notes magazine looks at the history of the flat tax, how it compares to our current tax system, and what the proposed flat tax plans would mean for the U.S. economy.