FORTUNE -- The super-rich got an early Christmas gift in the $858 billion tax package that President Obama signed into law on Friday. On top of a two-year extension of Bush-era income tax rates, the wealthiest Americans dodged an estate tax that was set to jump up from zero to 55% for individuals worth more than $1 million. Instead, under a deal Senate Republicans negotiated with the White House, individuals can exempt estates up to $5 million and pay 35% beyond that. The exemption for couples is $10 million.
Official estimates pin the two-year cost of the adjustment at $68 billion, and it will shield all but about 3,600 estates from the levy, according to a projection by the nonpartisan Tax Policy Center.
The windfall for the well-heeled wasn't delivered out of thin air. Indeed, a small band of the richest Americans have acted as their own secret Santas on this issue for years. A 2006 report by Public Citizen and United for a Fair Economy -- both nonprofits opposed to concentrated wealth -- identified 18 families financing a coordinated campaign to repeal the estate tax altogether. Among the leading names behind that push: the Gallos (E&J Gallo Winery), the Kochs (Koch Industries), the Mars' (Mars Inc.), the Waltons (Wal-Mart (WMT, Fortune 500)), and the Wegmans (Wegmans Food Markets). At the time, the report estimated the families' collected net worth to be at least $185 billion, roughly equal to the market cap of Google (GOOG, Fortune 500) today.
Several of the families organized their efforts through an association called the Policy and Taxation Group. Lobbying disclosure laws don't require the group to list its members, and as such, it hasn't disclosed any of them since 1999. But disclosures show the group itself remains active, with two hired-gun lobbying firms on its payroll this year. One of those shops, Patton Boggs, separately shills for the Mars and Wegman families on the issue.
Small estates vs. large estates
Proponents of an estate tax repeal make their argument by citing the burden of the tax on people with significantly less money -- namely small business owners and family farmers. And a wide range of trade associations organized under the banner of the Family Business Estate Tax Coalition -- a group that includes the American Farm Bureau Federation and the National Federation of Independent Business -- has stayed active lobbying to scale the tax back. They argue the levy is so onerous that small to middle-sized concerns are frequently forced to sell just to pay the piper.
Independent analysts question the veracity of those claims. The Tax Policy Center, for example, concludes there is "little hard evidence [to suggest] that the impact of estate taxes on family farms and businesses is a major concern."
To the extent smaller family businesses have weighed in on the debate over the tax, they have focused on bumping up the exemption, for obvious reasons: for most of them, a higher threshold means they won't have to pay anything.
It's a different story for families who need nine digits, or more, to tally their worth. That group has focused on driving down the rate, since a couple extra million dollars in exempted value amounts to chump change for them, while shaving percentage points off the tax quickly adds up to a lot more money.
Michael Graetz, who chronicled the lobbying effort against the tax in his book Death by a Thousand Cuts, says when the two camps came together in the 1990s, they could only find common cause around a full repeal. Graetz argues that dynamic shaped the bizarre schedule prescribed by the 2001 Bush tax cuts, whereby the tax wound down from a $675,000 exemption and 60% top rate that year to this year, when there was no estate tax at all.
It's not over yet
With a snap back to a much tougher rate looming on Jan. 1, repeal champions rallied around an approach advanced by Democratic Sen. Blanche Lincoln (Ark.), who counts the Waltons as constituents, and Republican Sen. Jon Kyl (Ariz.). The White House agreed to include that approach in the massive tax package apparently without putting up much of a fight -- a concession that still has many Congressional Democrats fuming.
But Vice President Joe Biden, appearing Sunday on Meet the Press, said the administration is already looking ahead to the next round of the debate: "The one target for us in two years is no longer extending the upper income tax credit for millionaires and billionaires, and scaling back what we had to do to get the compromise, the estate tax for the very wealthy."
Graetz says proponents of the tax need to start making a moral argument in favor of it, noting that it is fair, and -- in a time of the biggest deficits since World War II and the greatest income disparity since even earlier -- justified.
With an eye still fixed on full repeal, opponents are readying their case, as well. In the short term, they will be focused on preserving and possibly expanding the gains they made in the just-signed tax package. One argument they are already making: the 35% rate sensibly brings the tax in line with those on income.