House Budget Committee Chairman Rep. Paul Ryan, R-Wis., speaks at the Heritage Foundation in Washington, Wednesday, Oct. 26, 2011. 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/Jacquelyn Martin)