Mr. Saez and Mr. Zucman’s work shows that the wealthiest 0.1 percent of families — roughly the group that would be hit by Ms. Warren’s proposed tax — now hold 20 percent of all wealth in the United States. Their share of the nation’s wealth has doubled since 1985. In a recent sign of billionaire prosperity, the hedge-fund manager Kenneth Griffin paid $238 million for a Central Park apartment this week, more than doubling the previous record for a home purchase in the United States.

The bottom 90 percent of Americans by net worth hold 25 percent of all wealth, combined, according to Mr. Saez and Mr. Zucman’s work. That is down from nearly 40 percent of all wealth in 1985.

While the idea of taxing wealthy Americans is resurgent, it is not unique: The top marginal income tax rate in the United States was as high as 91 percent in the early 1960s. Today, the top marginal income tax rate is 37 percent, down from 39.6 percent during Mr. Obama’s second term.

Ms. Warren appears to be the first declared Democratic candidate to release a plan for a wealth tax, but the idea is quickly gaining steam among liberal activists and policy experts. Two left-leaning think tanks, the Institute on Taxation and Economic Policy and the Washington Center for Equitable Growth, released wealth-tax-themed policy briefs this week in Washington.

In a sign of the idea’s rising currency with the Democratic establishment, Ms. Batchelder and another former economic adviser to Mr. Obama both praised the plan on Thursday. “The incidence of extreme wealth inequality — as well as the magnitude of never-taxed wealth — is just so obscene at this point in our nation that I think there is simply no choice but to explore a wealth tax like this,” said Gene Sperling, who directed Mr. Obama’s National Economic Council.

The projected revenue from Ms. Warren’s proposal would be enough to pay for several policy initiatives that she and other Democrats have proposed, including universal prekindergarten, a $1 trillion federal infrastructure spending push and widespread debt relief for student loans. But increasingly, liberal activists see taxing the incomes and the wealth of the rich as a policy goal in and of itself — in order to combat what they see as dangerous levels of inequality.

“Democracies become oligarchies when wealth is too concentrated,” Mr. Saez said in praising the plan. “A progressive wealth tax is the most direct policy tool to curb the growing concentration of wealth in the United States.”