Is the flat-tax idea here to stay?

WASHINGTON -- The flat tax is making a comeback among Republican presidential candidates. But it faces tough opposition in Congress because it tends to favor the rich at the expense of other 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 proposal, and Texas Gov. Rick Perry this week unveiled a 20 percent flat tax on income. Even Romney foresees a flatter tax system.

The flat-tax idea has long been championed by conservative politicians as being simple and fair. Conservative economists argue it would promote long-term growth by lowering taxes on the people who save and invest the greatest share of their income: the wealthy.

Lowering taxes on the wealthy, however, could prove politically difficult, especially now, with protesters around the country occupying public spaces and calling for the rich to pay more. President Barack Obama and many Democrats in Congress also want higher taxes for the highest-income Americans.

Flat-tax plans by both Cain and Perry have provisions to protect low-income families from tax increases. But that raises questions about who will be left to pay the tab, said Roberton Williams, a senior fellow at the Tax Policy Center, a Washington think tank. "If you exempt the low-income people from higher taxes, if you cut the taxes for the wealthy, getting the same amount of revenue means the middle class are going to pay more, a lot more," Williams said. -- AP