FILE - In this Oct. 22, 2011 file photo, Republican presidential candidate, businessman Herman Cain speaks in Des Moines, Iowa. The flat tax is making a comeback among Republican presidential candidates. Most of the contenders _Mitt Romney's an exception _ offer a variation of the tax plan under which everyone pays the same rate. But a flat tax faces tough opposition in Congress because it tends to favor the rich at the expense of others. (AP Photo/Nati Harnik, File)