In 1995, Edward Wolff, an economist at N.Y.U., published a short book called “Top Heavy,” which detailed the increasingly alarming concentration of wealth in the United States, and warned of the threat that it posed to American democracy, as the ultra-rich sought to exercise more political power. At the time, the richest one per cent of families controlled about forty per cent of all household wealth—defined as stocks, bonds, other financial assets, equity in private businesses, trusts, real estate, and bank deposits—while much of the population had virtually no wealth at all once debts and mortgages were taken into account. To address this disparity, Wolff called for the introduction of an annual tax on wealth. Aware that this might be considered a radical idea, he kept his proposed tax rates at pretty low levels. Under his plan, households with a net worth of a hundred thousand dollars would pay five cents in tax on every hundred dollars of their wealth; the rate would rise to thirty cents per hundred dollars for households worth a million dollars or more. (Back then, about three per cent of U.S. households fell into the latter bracket.)

Despite the modest scale of Wolff’s proposal, it didn’t get much traction in the policy world. Prior to publishing the book, he did have a lunch meeting with Bill Bradley, the Democratic senator from New Jersey, where they discussed the idea, but that was as far as it went. “He sounded enthusiastic at the lunch, but when push came to shove he walked away,” Wolff recalled when I spoke with him earlier this week. “He thought that politically it was dynamite.”

Twenty-five years later, how have things changed? Last week, Senator Elizabeth Warren, the Democratic Presidential candidate, put forward a wealth tax that would be much bigger than the one Wolff proposed but also much more narrowly focussed. Under Warren’s plan, the tax rate on wealth would be two per cent, but it would only apply to American households worth at least fifty million dollars, of which there are fewer than eighty thousand. Fortunes of a billion dollars or more would be taxed at three per cent—ten times the top rate in Wolff’s plan. Not everyone is thrilled about Warren’s proposal, of course. During a visit to New Hampshire, Mike Bloomberg, who is considering running for President in 2020, as a Democrat, claimed that Warren’s proposal was unconstitutional and brought up Venezuela. Howard Schultz, the former Starbucks C.E.O. who is thinking of entering the Presidential race as an Independent, called the Warren plan “ridiculous.” On Capitol Hill, meanwhile, Mitch McConnell and two other Republican senators said that they would introduce a bill to repeal the federal estate tax, a type of wealth tax that has already been so weakened that it now hits fewer than two thousand families a year. So much for billionaires and Republicans.

But many moderate and progressive Democrats, far from recoiling from the Warren proposal, enthusiastically embraced it. “Wealth inequality in our nation is a national scandal,” Gene Sperling, a veteran Democratic policy wonk who served as a top economic adviser to Bill Clinton and Barack Obama, wrote on Twitter. “This type of wealth tax that @SenWarren is proposing is essential. It frees up dramatic amounts of resources that make it more likely the vast number Americans can have economic security & a shot at their own small nest egg.”

Since the publication of “Top Heavy,” the share of income and wealth going to the top one per cent, and especially the top 0.1 per cent, has risen a good deal further, while the wages and incomes of regular American households have stagnated. Meanwhile, the Citizens United ruling, the rise of super PACs, and the lurch to the right of the Republican Party and, of course, the Trump Presidency have demonstrated the growing political power of the billionaire class, throwing into sharper relief Wolff’s point that “the current tax system in the United States leaves these vast differences in wealth and power largely untouched.” Seth Hanlon, another former economic aide to Obama, who is now a senior fellow at the Center for American Progress, told me, “It is essential that we do something bold to get at our tax code’s failure to tax major accumulations of wealth. It is terrific that she”—Warren—“has put it on the table.”

In many policy circles, where taxing wealth is widely seen as an idea whose time has come, the debate is shifting to practicalities. Bill Gale, a senior fellow at the Brookings Institution, who worked at the White House Council of Economic Advisers under President George H. W. Bush, told me that taxing wealth more effectively can be justified on at least four different grounds: equity (in some cases, as Warren Buffett famously pointed out, the very richest American households pay a smaller share of their income in tax than middle-income households do); revenues (even though the unemployment rate is at a historic low, the budget deficit stands at more than 4.5 per cent of G.D.P.); “rent-seeking” (by manipulating compensation committees, many C.E.O.s effectively set their own compensation); and the desire to prevent the further emergence of a plutocracy. (By some estimates, the top 0.1 per cent now controls almost as much wealth as the bottom ninety per cent of households.) “I am sympathetic to the idea of a wealth tax,” Gale said. “It is certainly not a crazy notion, but I don’t know if it would work.”

Part of the problem is that other countries have shown that wealth taxes create incentives for rich people to evade them by sheltering or hiding assets, or, in extremis, by emigrating. France and Denmark both got rid of wealth taxes on investments and other non-property assets, partly because they didn’t raise as much money as was hoped. Gabriel Zucman and Emmanuel Saez, two Berkeley economists who provided a detailed assessment of the Warren tax plan, estimate it would raise $2.75 trillion over ten years, which is a very large sum. But Wojciech Kopczuk, an economist at Columbia University who has studied the estate tax extensively, told me that the $2.75 trillion figure is “wildly optimistic.” If Warren’s tax were enacted, Kopczuk said, many wealthy families would divide their wealth among themselves to stay under the fifty-million-dollar threshold, and they would also start shifting their wealth into assets that are hard to value, such as collectibles and privately held businesses. “I think that they”—Saez and Zucman—“are assuming that there is more wealth than there is, and they are underestimating the amount of tax planning that will take place,” Kopczuk said. “I am sure that the tax lawyers and tax accountants have ideas already.”

Economists who have looked into tax avoidance have reached differing conclusions. A recent study of Switzerland, which has long administered a wealth tax at the level of individual cantons, found that a “0.1 percentage-point increase in wealth taxes leads to 3.4% lower wealth holdings in the cross canton data.” That’s a big impact. “When you tax people’s wealth, they manage to somehow reduce their taxable wealth,” Jonathan Gruber, an M.I.T. economist who was one of the authors of the study, told NBC News. “We don’t know if it’s by saving less or by hiding it.” Gruber added, “Elizabeth Warren’s tax would raise money, it’s a question of how much.”