In the early 20th century, there was nearly an opportunity for the high court to reverse its earlier decision, which barred most wealth and income taxes. Democrats in Congress wanted to pass an income tax law to "challenge the court to strike it down again," according to Ackerman.
But President William Howard Taft, a Republican who would later become the only president to also serve as chief justice of the Supreme Court, feared that such a challenge could spark a constitutional crisis.
"Taft, who was newly elected and was very much a protector of the court, thought that if the court does this they will commit suicide," Ackerman said.
So to avoid a skirmish, Taft pushed for the passage of the 16th Amendment to the Constitution. That amendment permits Congress to "lay and collect taxes on incomes" without regard to state populations.
That ended the controversy over taxes on income. But debates over whether Congress can tax wealth without apportionment among the states still linger. The distinction between income and wealth is important, as most of American economic inequality is in wealth disparities, not income.
"The wealth tax is not affected by the 16th Amendment," said Princeton University's Franck. "To say that you can go after wealth itself is a wholly different tax that the 16th Amendment doesn't address."
Ackerman and others dispute this, arguing that the intention of the 16th Amendment was to overrule the Supreme Court's 1895 decision.
"Any originalist confronted with this legislative history would recognize that the will of the American people was to sweep away this aberrational decision and the kind of reasoning it represented," Ackerman said.
Franck said that such "extra-textual insight" was creative, but "you can't derive that from the text."
"It's not what a textualist would say," he said.
Still, even for experts who back wealth taxes in general, there are concerns that a proposal like Warren's would face the daunting task of amending the Constitution. Three-fourths of the states must ratify a constitutional amendment after it is backed by two-thirds of each chamber of Congress.
Thomas Piketty, author of "Capital in the Twenty-First Century" and one of the leading economists in the world, has endorsed Warren's proposal. In 2014, he said of an American national wealth tax that he realized that "this is unconstitutional."
"But constitutions have been changed throughout history," he said. "That shouldn't be the end of the discussion."
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