The estate tax has long punched above its weight. Despite applying to less than one-half of 1% of U.S. estates each year–mostly the richest of the rich–it has earned outsize attention in the political ring, often the subject of presidential campaigns, legislative horse-trading and philosophical scrimmages over the proper role of taxes in the Republic. Democrats see it as a populist measure designed to prevent the accumulation of dynastic wealth, while Republicans, who masterfully rebranded it as the “death tax” in the early 1990s, decry it as a penalty on success. With a comprehensive tax-reform bill widely expected to come down the pike in 2017, the battle over the estate tax will likely be at the forefront yet again–with Republicans poised for the first time in more than a decade to land a mortal blow.

Both President-elect Donald Trump and House Speaker Paul Ryan have promised to scrap the estate tax as soon as they can. But neither has yet provided much detail on how, exactly, they’ll pull that off. Will they offset a decline in revenue with an increase in capital gains? When, exactly, would a repeal of the estate tax go into effect?

As of 2016, the rules are clear: upon a married couple’s death, the first $10.9 million of their estate is shielded from tax; everything that exceeds that amount is subject to a 40% rate. (For individuals, the first $5.45 million of an estate is shielded and the rest taxed at 40%.) Because of those high exemption rates, roughly 99.6% of Americans who died in 2016 didn’t pay estate taxes at all. In 2015, the IRS processed just 4,918 taxable returns for the estate tax out of 2.6 million deaths. Of those, the superrich–think the children of storied American bloodlines, like the Waltons, Kochs, Buffets or Trumps–paid the most. Two hundred and sixty-six families reported $37.6 billion in taxable assets, according to Treasury data. “That’s where that 40% rate starts to look like real money,” says Michael Graetz, a professor at Columbia Law School and a leading expert on tax law.

Conservatives argue that the estate tax is both unfair, since it extracts large revenues from a sliver of the tax base, and detrimental to the economy. If Trump and a GOP-led Congress nix the tax, thus freeing up the very wealthy to reinvest their billions, and tinker with capital gains, U.S. GDP could increase by 0.7% over 10 years and usher in across-the-board wage growth, according to Stephen J. Entin, a senior fellow at the Tax Foundation.

Democrats say that’s wishful thinking. While the estate tax is often described by critics as a levy on farms and family-owned businesses, Treasury data shows that most of the time it applies to large estates and inherited securities, like stocks, bonds and private-equity funds, where reinvestment often has little effect on wage growth. Democrats also argue that getting rid of the estate tax would create a $269 billion hole in federal coffers over the course of a decade. While that represents just under 1% of total federal government revenues, it’s enough to underwrite the combined 2016 budgets for the Departments of State, Education, Labor, Transportation and Justice, according to the National Priorities Project.

In the tax plan on his website, Trump offers to offset these losses in part by eliminating exemptions elsewhere, but it’s unclear how it would work. “There’s zero detail,” says Jay Freireich, a New Jersey–based tax and estates attorney.

Another elephant in the room, says David Lifson, a federal tax-services partner at Crowe Horwath, a large public accounting firm, is whether the repeal of the estate tax would lead to a decline in charitable giving. As of now, the very wealthy face an option at the end of their lives: they can either bequest a portion of their estates to a philanthropic fund, like a civic arts program, university, or museum, or face a hefty tax bill after death. Many on both ends of the ideological spectrum worry that axing the estate tax will remove the financial incentive to give money away. There is some evidence, for instance, that when the higher exemption rates for the estate tax were set to expire in 2013, gifts from wealthy donors surged dramatically, reaching roughly $440 billion in 2012. When President Obama and a Republican-led Congress reached the so-called grand bargain later that year, extending the exemptions, gifts fell to the normal annual rate of about $30 billion the following year.

It was in 1916, exactly 100 years ago, that the estate tax was first imposed, championed by the populist former President Teddy Roosevelt, who worried about the effect of concentrated wealth. Ironically, a century later, it’s another populist revolution that promises to do it in.

This appears in the December 12, 2016 issue of TIME.

Sign up for Inside TIME. Be the first to see the new cover of TIME and get our most compelling stories delivered straight to your inbox. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Haley Sweetland Edwards at haley.edwards@time.com.