The Buffett Tax, because it won't raise revenue, should be understood mostly as Election-Year demagoguery. And like most demagoguery, it is not well grounded in facts.

The basic argument is that the rich don't pay their fair share in taxes. Rather than data, President Obama relies on anecdote -- that Warren Buffett supposedly pays taxes at a lower rate than his secretary does. Let me present some data to the contrary.

First, below is a chart from CBO data showing who pays their "fair share" in federal individual income taxes, if fair share is defined by the Marxian saying, "from each according to his means."

Each cluster is a quintile of the U.S. population. The 20 percent earning the least gets a net profit from the federal income tax. The second quintile as a group pays nothing. For the middle and fourth quintile, you'll see that the green bar -- their share of all income earned in the U.S. -- is much bigger than their red bar, which is their share of all individual income taxes paid to the IRS.

Only the richest quintile pays more than its share, and it pays far more than its share. Earning 56% of all income, this quintile pays a whopping 86% of all the federal individual income taxes.

The standard liberal response is that I'm being misleading because I'm only looking at federal individual income taxes, which for many people is a small portion of their tax burden. I'm unimpressed with this line of argument, though. If liberals don't like the distributive effects of FDR's Social Security Tax or LBJ's Medicare tax, they should change those laws, rather than try to further jury-rig the tax code. 

But even so, insert the payroll taxes (and to be fair, other federal taxes) and you get a flatter distribution, with the same basic theme: the bottom four quintiles take a greater share of the nation's income than the share they pay of federal taxes (their red bars are all shorter than their green bars). Meanwhile the top 20% pay far more than their proportionate share.

But what about the very rich? Maybe they're just rich enough to get out of taxes? Well, I agree that tax-code complexity favors the wealthy, but still, the top 1% pays a higher portion of federal taxes than it makes in income.

So there's still a debate. Proportional share and fair share aren't the same thing. But at least the administration should make an argument as to how to determine "fair share."