FILE - In this Oct. 13, 2011 file photo, Republican presidential candidate former Massachusetts Gov. Mitt Romney speaks in Redmond, Wash. 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/Elaine Thompson, File)