The other day, economist Gabriel Zucman of the University of California at Berkeley put out a new paper that startled many observers, finding that wealth inequality has returned to levels not seen since the 1920s.

The paper’s key attention-grabber: The 400 richest people in America now own a greater share of the nation’s wealth than the bottom 150 million people do.

As Christopher Ingraham summarized, this remarkable finding may understate the severity of the situation. The ongoing wealth shift is having serious consequences, eroding the economic security of untold numbers of ordinary families, while further consolidating economic and political power in the hands of a tiny economic elite.

Zucman is one of the world’s leading trackers of inequality. When Sen. Elizabeth Warren introduced her proposal for a tax on extreme wealth — of 2 percent on wealth over $50 million, and 3 percent over $1 billion — it was accompanied by an analysis from Zucman.

Warren’s wealth tax proposal is only one of many from Democratic presidential hopefuls. Warren has rolled out reforms to make big corporations more responsive to the public interest and a plan for universal child care. Others are advocating ambitious tax credits for the working poor and children. Sen. Bernie Sanders is pushing a raft of proposals to curb corporate power and boost worker power, among other things. Also on the table: a $15-per-hour minimum wage and variations of Medicare-for-all.

In short, the Democratic field is now more focused on inequality and concentrated economic and corporate power than any presidential field in recent memory. I spoke to Zucman about his findings and what lies ahead, and a transcript of our conversation, edited for length and clarity, follows.

The Plum Line: Your new report talks about the fact that inequality is back up to Gilded Age levels.

Gabriel Zucman: What the data show is that wealth concentration in the United States has returned to the level of 1920. Forty percent of total household wealth belongs to the top 1 percent. About 20 percent belongs to the top 0.1 percent, which is about the same as the bottom 90 percent’s wealth share. What’s happening in the United States is pretty unique among developed countries.

Plum Line: We haven’t seen this for nearly 100 years. This seems to be why we’re now seeing the most robust set of policies in response to inequality from presidential candidates in an extremely long time.

Zucman: I think that’s correct. The growing realization that wealth concentration has returned to Gilded Age levels is the primary reason why we see these proposals for increased tax progressivity, and why we’re finally having a debate about wealth taxation.

Plum Line: When is the last time we saw proposals quite this targeted at inequality in particular?

Zucman: The clear analogue is the creation of the federal income tax in 1913. In the Gilded Age, there was also a big increase in income and wealth inequality, and with it, a growing popular demand for progressive taxation. The similarity is striking.

Plum Line: At that time, and with the New Deal, you saw a coming together of a new aggressiveness toward inequality that had been advocated on the left for many, many years. It’s a little different now. We haven’t had the same kind of long-running intellectual ferment on the left, although we’re now seeing it.

Zucman: The tax debate since the 1980s has been almost exclusively about tax cuts, and it has taken a long time for democracy to break from this framing. But when you look at public opinion polls, they consistently show that vast majorities fully support higher taxation on the wealthy. What’s happening is that the Democratic Party is moving toward the electorate.

Plum Line: The parallel here is the advent of the income tax a century ago. But that ended up leading — though the financial crash also propelled this — to a much broader set of reforms in the form of the New Deal. Do you think it’s conceivable that we’re at the start of an era of long-range transformation of our political economy?

Zucman: That’s possible. It’s certainly what’s happened historically. Progressive taxation typically comes with other progressive policies. And vice versa: When progressive taxation was curtailed in the 1980s, that was accompanied by reductions in the minimum wage and the power of unions.

Plum Line: You can look at the 1980s as the beginning of a debate in which we were told that unshackling the economy through deregulation and tax cuts would benefit everyone. Yet what we saw was a kind of triumph of the super-rich that was much more dramatic than anyone expected.

Zucman: The United States has run an unprecedented social experiment since the 1980s — slashing the tax rate, deregulating finance and labor markets, cutting the minimum wage, and so on. Almost 40 years after the start of this experiment, we have the data to judge whether this experiment was successful or not.

What we are seeing is that for the bottom 50 percent of the income distribution, their average income was $16,000 a year per adult in 1980, adjusted for inflation. And it’s still $16,000 a year per adult today. The bottom half of the income distribution, on a pre-tax and -transfer basis, has had zero growth for more than a generation. What’s the lesson that we can draw from this experiment, and how can we do better?

Plum Line: Very powerful interests believe that this experiment was a smashing success.

Zucman: That is true. But the same was true in 1913 — and yet the Constitution was changed and a progressive income tax was introduced, which quickly became very progressive with top tax rates of 70 percent or more. This historical precedent makes me relatively optimistic about the prospect of substantial tax policy changes in the years to come, and in particular about the possibility of wealth taxation.

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