Now that some opinion polls have Herman Cain leading the race for the Republican nomination, it is time to take a closer look at his “9-9-9” economic plan, which is the centerpiece of his campaign. For those of you who are in a hurry, here is the takeaway:

It doesn’t raise enough revenue. Without offsetting cuts in spending, it would send the budget deficit skyrocketing.

It would be extremely regressive. Poor and middle-income people would pay higher taxes. Rich people would pay a lot less.

Its impact on growth is debatable.

Let’s start with Cain’s campaign Web site, which lays out the bare bones of the plan on a single page. If you think this isn’t very much for a proposal that would junk the entire tax code, you are right. Still, here’s what Cain has to say. The plan has two phases:

Phase 1: “9-9-9” Abolish the payroll tax, which pays for Social Security and Medicare, the capital-gains tax, inheritance taxes, and taxes on dividends. Abolish the graduated income tax and replace it with a flat tax of nine per cent. Abolish the graduated corporate income tax and replace it with a flat tax of nine per cent. Introduce a new nine-per-cent national sales tax.

Phase 2: “The Fair Tax.” What is this? It isn’t defined, but it appears to involve making the Phase 1 changes permanent. Cain simply says, “Amidst a backdrop of the economic boom created by the Phase 1 Enhanced Plan, I will begin the process of educating the American people on the benefits of continuing the next step to the Fair Tax. The Fair Tax would ultimately replace individual and corporate income taxes. It would make it possible to end the IRS as we know it.”

The key to the plan’s appeal is its simplicity. Rather than waiting until after next year’s election, he is calling on the congressional “super committee” to introduce Phase 1 now. “America can’t wait for 2012,” he says. “We need growth NOW.”

Surely, we do. But how would Cain’s plan work in practice? In addressing any tax proposal, it is important to look at its likely impact on three things: fiscal sustainability (how much money would it raise?); income distribution (who would benefit and who would lose?); and economic growth.

Up until now, Cain hadn’t provided any figures or projections to answer any of these questions. Yesterday, however, Rich Lowrie, a wealth manager from Cleveland whom Cain referred to in Tuesday’s debates as somebody who had worked on the 9-9-9 plan, told Bloomberg it would have raised about $2.3 trillion in 2008, which is roughly what the existing tax system raised. Of that $2.3 trillion figure, about $860 billion would have come from businesses, $700 billion from individual income taxes, and $750 billion from the sales tax, Lowrie said. Apparently, these figures were put together by a financial advisory firm called Fiscal Associates, which is based in West Bloomfield, Michigan.

Are they credible? The figures for income taxes and the sales tax are higher than but roughly in the same ballpark as estimates from independent experts. But Cain’s $860 billion figure for business taxes seems very, very high. In a critical analysis of Cain’s plan, Michael Linden, the director of tax and budget policy at the Center for American Progress, has estimated that in 2007 a nine per cent corporate flat tax would have yielded $112 billion—almost $750 billion less than Cain’s estimate for 2008!

Linden calculates that under the Cain structure overall federal taxes in 2007 would have totaled about 9.5 per cent of G.D.P., which is barely half the actual figure of 18.5 per cent. “Even if we reduced federal spending to the ‘historical average’ (when the population was younger and health care cost much less) it would still leave us with deficits over 11 percent of GDP (bigger than any deficit since WWII, including the deficits of the past three years),” Linden noted.

What about the distributional question? On the face of it, reducing the federal income-tax rate to nine per cent sounds like a big pay cut for the average person. But that is misleading. Under the current federal tax system, almost everybody is allowed to deduct from their gross income a $5,800 standard deduction and a $3,700 personal exemption. On top of that, there is the child credit, the child-care credit, the earned-income tax credit, the mortgage interest deduction, and various other deductions—all of which serve to reduce the effective tax burden. Cain would do away with all of this, and he would also impose a nationwide sales tax on everything from bread to clothes to cars.

Consequently, a lot of Americans would end up paying higher taxes. How much higher? According to a new analysis by Edward D. Kleinbard, a former staffer at Congress’s Joint Committee on Taxation, a typical family of four with $120,000 in wage income would face an annual tax increase of $800. Many poorer Americans would face a much more substantial tax hike. Under the current system, with its various deductions and tax credits, many poor and middle-income families pay little or no federal income tax: their federal tax burden consists mainly of the payroll tax. Under Cain’s plan, there wouldn’t be a payroll tax, but all families would have to pay the new nine-per-cent rate on their income, and they would also have to pay the new nine-per-cent sales tax. Take a family earning about $50,000 a year, which isn’t far from the median household income. All told, it could face tax a hike of $2,500, or even more, according to some estimates.

As for the richest people in the country, who earn much of their income in the form of interest, dividends, and capital gains generated by their existing capital, they would benefit enormously from the abolition of the capital-gains tax and the tax on dividends that Cain proposes. According to Linden, a typical Americans in the richest one per cent would see his tax rate fall from twenty-eight per cent to eleven per cent. Other tax experts using slightly different classifications nonetheless come up with similar figures. Roberton Williams, of the non-partisan Tax Policy Center, tells the Christian Science Monitor that the effective tax rate on people in the highest tax bracket would fall from twenty-one per cent to nine per cent. In short, the Cain plan would involve an unprecedented shift in the tax burden from the rich to the middle class and the poor.

That leaves the plan’s impact on growth. In cutting overall federal taxes, it could give a boost to demand. But since the tax cuts would be focussed on the rich, who tend to spend less of their income proportionately, the normal Keynesian effect would be dampened. And if the prospects of even higher deficits spooked the bond markets, it could disappear completely. Cain, of course, makes the supply-side argument that raising the returns to risk-taking would spur investment, hiring, and productivity growth. Without any actual economic projections to look at, it is hard to evaluate. If you are disposed to believe this argument, there is probably nothing I could say to dissuade you, anyway.

So far, Cain has benefitted greatly from being the only candidate with a simple, snappy economic plan. As it receives more attention, this may well change. For example, consider seniors—a category of the population in which Cain appears to be polling well, especially in states like Florida. Do these folks realize he is proposing to hit many of them with a tax hike? Today, most seniors don’t pay payroll taxes, and they have moderate incomes. Consequently, their tax burden is low. Under Cain’s plan, whatever income seniors receive would be taxed at nine per cent, and so would their expenditures. In Florida, the sales tax on early-bird specials would jump from six per cent (the state sale tax) to fifteen per cent.

Wait until they figure that out in Sarasota and Fort Lauderdale!

Photograph by Daniel Acker/Bloomberg via Getty Images.