A new study of the intensifying concentration of wealth in the United States reveals that the 400 richest people in the nation just .00025 percent of the population own more than the 150 million adults in the bottom 60 percent, according to an analysis by The Washington Post.

The information on the richest Americans, in a working paper by University of California at Berkeley economist Gabriel Zucman, comes as pressure appears to be mounting among American taxpayers to increase taxes on the countrys ultra wealthy.

Zucmans study, Global Wealth Inequality, released last month, also found that the 400 richest Americans tripled their wealth since the early 1980s.

The share of the nations wealth held by the adults in the bottom 60 percent, meanwhile, dropped from 5.7 percent in 1987 to 2.1 percent in 2014, the Post reported, citing the World Inequality Database thats maintained by Zucman and other economists.

U.S. wealth concentration seems to have returned to levels last seen during the Roaring Twenties, Zucman wrote. And as wealth begets power the political system is impacted, he noted.

Zucman has advised Rep. Elizabeth Warren (D-Mass.) on her plan to impose an annual wealth tax on people with $50 million and more in assets. Three online polls early this month showed support for her plan running from 50 percent to as high as 61 percent .

Rep. Alexandria Ocasio-Cortez (D-N.Y.) has also talked of boosting the marginal income tax rate to 70 percent for the portion of income exceeding $10 million a year. The majority of Americans support raising taxes on the wealthy, according to polls. A survey early this month found that 76 percent of registered voters support raising taxes on the wealthiest.

Zucmans study compared net worth not income which is the value of everything that a family owns, minus debt. Homes, land, rental properties, stock, bank accounts and any business holdings are all included. Personal possessions, like cars, were not included.