Sen. Elizabeth Warren has set the stage for a colossal battle at the U.S. Supreme Court over her proposed wealth tax on households worth more than $50 million.
The proposal, which would raise trillions of dollars to fund a host of social programs that are key to the Massachusetts senator's agenda, would awaken an area of constitutional law that has lain dormant for decades, experts say.
And it would put Warren, if elected president, on an early collision course with a branch of government that could determine the success or failure of her administration.
It is a concern the campaign is aware of. Behind the scenes, Warren's team sought legal advice from leading scholars ahead of rolling out its proposal, and put together a deeply researched briefing book on the matter.
But that work was likely just the start of a long process that is shaping up to be the first major legal test of a candidate who was once an influential professor at Harvard Law School.
"It's the dream of constitutional law professors," Matthew Franck, associate director of the James Madison Program in American Ideals and Institutions at Princeton University, said of Warren's proposal. "It would be an occasion for a burst of amicus briefs, of scholarly articles, of all sort of scholarly arguments."
But it could be a nightmare for a nascent administration butting heads with a conservative court over a tax that Warren has said she would use to provide funding for investments in child care, reductions of student loan debt and an ambitious slate of climate policies.
The proposal would impose a 2 percent tax on net worth between $50 million and $1 billion. A 3 percent tax would apply to household net worth above $1 billion. In total, according to the proposal, Warren's "ultra-millionaire tax" would raise $2.75 trillion in revenue over a 10-year period from fewer than 80,000 families.
Bruce Ackerman, a prominent constitutional scholar who provided Warren with legal guidance on the proposal, said he did not know how the justices would come down on the matter. But, he said, their decision would ultimately be a "test of seriousness."
"A lot depends on whether they will pass the test," Ackerman said. "We have to give them a chance to consider deeply these issues."
In response to inquiries, an aide to Warren pointed to letters from legal scholars supporting the plan. Those letters, which buck the conventional wisdom regarding the constitutionality of a wealth tax, include ringing endorsements from noted scholars including former top lawyers in the Department of Justice.
But even those who have advised Warren on the legality of the plan are uncertain about what the nation's top court might do.
The question of whether a wealth tax is lawful stems from the Constitution's ban on any national "direct" tax that is not collected evenly from the states based on their populations.
That language originated in a compromise over slavery. In exchange for receiving extra representation in Congress through the census' enumeration of each enslaved black person as three-fifths of a free person, the slave-holding states were required to ante up a corresponding amount of tax dollars.
For more than a century after the Constitution was ratified, wealth taxes were not thought to be "direct" taxes, and versions were upheld. But that changed in 1895, when, in the midst of a barrage of anti-populist rulings, the Supreme Court for the first time declared a wealth tax unconstitutional.
"We have acknowledged in our discussion that there is a case remaining on the books that would seem to make it unconstitutional," said Walter Dellinger, a law professor at Duke who also consulted with Warren on the proposal. "It is from an era where the court was striking down any progressive legislation, including minimum wage laws and maximum hours laws."
While the court later reversed itself on minimum wage and maximum hours laws, there has been no such reversal on a wealth tax. Dellinger said that he believed the court, as presently constituted, would do just that.
"But who knows how the court will be constituted when a wealth tax actually comes before it," he said.
Dellinger and Dawn Johnsen, a law professor at Indiana University, published an article last year "to help ensure that a wealth tax is among the policy options available to Congress." Members of Warren's staff studied the article as they prepared to release their proposal.
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."