Flat tax renews fight on 'trickle-down economics'

WASHINGTON (AP) — The flat tax is making a comeback among Republican presidential candidates, but it would face tough opposition in Congress. It tends to favor the rich at the expense of the rest of taxpayers, renewing an old debate about "trickle-down economics."

Most of the top GOP contenders — Mitt Romney's an exception — offer a variation of the tax plan in which everyone pays the same rate. Businessman Herman Cain has his 9-9-9 tax proposal, and Texas Gov. Rick Perry unveiled a 20 percent flat tax on income this week.

The idea of a flat tax has long been championed by conservative politicians as being simple and fair. Liberals and many moderates contend a flat tax is a giveaway to the rich.