America's "progressive" income tax takes a larger percentage from high earners than those lower down on the scale. At the moment, there are six tax "brackets," ranging from 10 to 35 percent. Republican presidential candidates Herman Cain and Rick Perry want to replace "progressive" taxation with new versions of the so-called "flat tax," which begins with the idea that all income should be taxed at the same rate. Abraham Lincoln levied the first "flat tax" to finance the Civil War. Since then, the idea's been revived by candidates of both parties, including California Democrat Jerry Brown, when he ran for president in 1992 and Republican Steve Forbes in 1996. What is the "flat tax?" Is it simple? Is it fair? Why do proposals often shift the burden from wealthy taxpayers to those in the Middle Class?