For decades now, Republican lawmakers have made eliminating the estate tax (or "death tax," as opponents call it) a top legislative priority. Just last week Republicans in the House voted to repeal it. They paint it as a simple issue of fairness. The tax, they claim, hurts small farms and family businesses, punishes savers, and hits income that's already been taxed once. "The 'death tax' is an immoral tax and an attack on the American dream," Reps. Kevin Brady (R-TX) and Steve Scalise (R-LA) write in USA Today. By contrast, liberals tend to argue that estate tax repeal is nothing more than a massive giveaway to the rich, or, as E. J. Dionne dubbed it, "the Paris Hilton tax cut."

It's all an awful lot of fuss over a pretty small tax. It raised only $19.3 billion in 2014, 0.6 percent of total federal receipts that year. The Congressional Budget Office estimates repeal would increase the deficit by almost $270 billion over 10 years — an increase of less than 4 percent, given that deficits are already expected to total $7.2 trillion over that period. The vast majority of Americans never pay the tax.

But the estate tax is more than just a normal revenue raiser. It's a flashpoint in debates about wealth inequality, and an important front in conservatives' battle against redistributive taxation.

What is the estate tax? How does it work?

An estate tax is a tax on the wealth of deceased persons before it's distributed to their heirs. In the US, the federal government exempts bequeathals to surviving spouses and charities from taxation. Beyond that, there's a large per-person exemption ($5.43 million in 2015, or nearly $11 million for married couples). A 40 percent tax is levied on the value of the estate (after deducting donations and spousal gifts and the like) in excess of the exemption amount.

In practice, estate-tax payers pay way less than 40 percent, due to the generous exemption and deductions:

The estate tax is usually considered in conjunction with the gift tax, which applies to gifts given in one's lifetime. That prevents estates from evading taxation by distributing money before death. The first $14,000 in gifts a donor makes to a specific donee every year is exempted, but beyond that gifts are taxed at estate tax rates.

How much does the estate tax raise?

Compared with income and payroll taxes, estate and gift taxes aren't a particularly large source of federal revenue, raising only $19.3 billion in 2014, 0.6 percent of total federal receipts that year:

However, receipts have varied considerably as the tax has changed. The Bush tax cuts of 2001 gradually phased out the tax until it was repealed in 2010. It was set to return in full in 2011, but a deal between President Obama and congressional Republicans cut it significantly from Clinton-era levels; Obama also got a small rate increase as part of the 2012 fiscal cliff deal, but the tax is nonetheless considerably lower than it was in the 1990s. The result is a fluctuating trend in revenue, with receipts hitting a low of $7.4 billion in fiscal year 2011 (which covers part of calendar year 2010, when the tax was repealed).

Supporters of the tax, while conceding that it doesn't raise much money relative to the budget as a whole, argue it still raises a significant amount. "While it’s less than 1 percent of federal revenue," the Center on Budget and Policy Priorities' Chye-Ching Huang notes, "that’s significantly more than the federal government will spend on the Food and Drug Administration, the Centers for Disease Control and Prevention, and the Environmental Protection Agency combined."

Who pays the estate tax?

The estate tax is the most progressive tax the federal government has. According to the Tax Policy Center, tax filers not in the top 5 percent — roughly, those making less than $200,000 in 2013 — pay a negligible percentage of their incomes in estate taxes. On average, people above that pay small percentages, too — most people don't die in a given year, after all — but they bear the overwhelming majority (93.1 percent) of the total estate tax burden. And nearly half of the estate tax burden is paid by the top 0.1 percent — taxpayers making more than about $2.6 million a year in 2013.

One caveat here: this uses income as of year of death, which doesn't account for investments people haven't cashed out on yet. So a person might appear to have a low income but actually be quite wealthy.

Another way to look at this is to consider what share of estates pay the tax. According to a Joint Committee on Taxation analysis, while nearly 2.6 million people died in 2013, only 4,687 estates faced taxation. That's only 0.18 percent of total deaths.

I thought the estate tax hit farmers and small businesses?

That's a common talking point of opponents of the tax. But it's hard to find much grounding for it in the data. A Tax Policy Center analysis found that in 2013, estates with small businesses and farms — that is, estates "where farm and business assets represent at least half of gross estate and these assets total no more than $5 million" — filed only 20 taxable returns. Let me repeat that: out of the 3,780 total taxable returns in 2013, TPC estimated that only 20 (0.5 percent) people with small businesses and farms were hit.

On average, these estates paid only 4.9 percent in tax. What's more, a 2005 analysis by the CBO found that under the 2009 estate tax, only 182 estates — and only 13 estates of farmers and 41 estates of people with family-owned businesses — wouldn't have enough liquid assets (bonds, stock, cash, etc.) to pay their estate tax liability. The current estate tax law is even more generous than it was in 2009, meaning it's likely even fewer estates are in that situation today. Moreover, as CBPP's Huang and Brandon Debot note, "special estate tax provisions — such as the option to spread payments over a 15-year period and at low interest rates — allow the few taxable estates that would face any liquidity constraints to pay the tax without selling off any farm assets."

Is the estate tax a form of double taxation?

Depends on how you look at it. Some income does get taxed twice. If you're a CEO, earn $5 million a year in wages for 10 years, and then leave it to your heirs, you get taxed both on your wages and on the bequest. But as Huang and Debot note, a lot of the wealth hit by the estate tax comes in the form of unrealized capital gains that would otherwise go untaxed.

Imagine you're living in New York in the 1980s and buy an original Basquiat painting for $200. By the time you die and leave that painting to your daughter, it's worth $40 million. If your daughter then sells it, she'll pay capital gains tax — but only on the difference between the sale price and $40 million. The tax code defines heirs' gain relative to the value of an asset when they inherit it, rather than its value when their bequeathers bought it.

This feature of tax law is known as "step-up basis," and many people, including the Obama administration, want to end it. But so long as it exists, the estate tax blunts its impact. Your daughter may not have to pay taxes on the $200 to $40 million gain, but you'll have to pay taxes on the gain if the painting is part of your estate. This isn't hypothetical, either. Unrealized capital gains like the Basquiat painting account for most of the assets claimed by large estates (ones bigger than $100 million):

Estate tax detractors might note that the $200 you used to buy the painting in the first place was after-tax income, so in a sense you're still being double-taxed. Indeed, if you were to sell the painting before death, pay capital gains tax on the gain, and leave the rest to your estate, you'd be triple-taxed on this logic. But if you support taxing capital income, estate tax charges on unrealized gains aren't really much different.

Do states have estate taxes?

Yup. Fifteen states, as well as DC, have estate taxes. This map from the Tax Foundation handily summarizes state laws as of 2014:

However, Tennessee is phasing out its tax, and Maryland, Minnesota, and New York are phasing in increases in their exemption levels, effectively cutting the tax. In addition to the estate tax states, there are six states with inheritance taxes, which tax heirs and other beneficiaries of estates rather than the estates themselves. Maryland and New Jersey have both estate and inheritance taxes.

Why is the estate tax such a big deal?

It may seem strange that a tax that more or less nobody pays and that raises little revenue would get this amount of attention. But there are a few complicating factors that help explain it.

One is that it's unpopular. Despite almost none of them having to pay it, most Americans tell pollsters they oppose the estate tax. Part of that is no doubt due to decades of Republican politicians reframing it as the "death tax" and casting it as an enemy of small-business owners and other sympathetic figures. This more cynical view got some support from recent studies showing that opposition to the tax declines when people learn how few estates are actually affected. But it also just strikes many people as intuitively unfair for people to not be allowed to leave the fruits of their labor to their children (though, as noted above, they're often not leaving the fruits of their own labor at all).

The second is that it's the main way the tax code addresses inequalities in wealth. Even since the English translation of Thomas Piketty's Capital in the 21st Century was released last year, there's been a shift in the debate around inequality from income to wealth, and growing concern that, as Piketty predicted, high returns to capital will result in ever-growing piles of wealth that are transmitted across generations, creating a permanent aristocracy with huge political power. But that only happens if the rich can reliably pass on huge estates. Estate taxes have the potential to break up huge wealth piles like that and prevent an aristocracy from forming. Piketty proposes bigger measures — like an annual tax on wealth, rather than one merely levied at death — but maintaining the estate tax is certainly helpful for his goals.