Required wealth tax results in economic stagnation, depresses business confidence and punishes efficiency.

But redirecting such vast sums could have unintended effects on the United States economy that go beyond promulgating economic fairness. While Ms. Warren ticks off the social programs that can be funded if the richest Americans pay just 2 cents on every dollar they have above $50 million — a number that is unimaginable to most Americans — skeptics warn of economic stagnation, depressed business confidence and a legal battle that would go to the Supreme Court.

At a conference sponsored by the Brookings Institution in September, N. Gregory Mankiw, a Harvard economist, debated Mr. Saez and Mr. Zucman about the merits of taxing wealth. Mr. Mankiw, the former head of President George W. Bush’s Council of Economic Advisers, offered a searing critique, arguing that a wealth tax would skew incentives that could alter when the superrich make investments, how they give to charity and even potentially spur a wave of divorces for tax purposes. He also noted that billionaires, with their legions of lawyers and accountants, have proven to be experts at gaming the system to avoid even the most onerous taxes.

Left-leaning economists have expressed their own doubts about a wealth tax. Earlier this year, Lawrence Summers, who was President Bill Clinton’s Treasury secretary, warned in an article with Natasha Sarin, a law professor at the University of Pennsylvania, that wealth taxes would sap innovation by putting new burdens on entrepreneurial businesses while they are starting up. In their view, a country with more millionaires is a sign of economic vibrancy.

“Turning the tax code into a vehicle for confronting what some call ‘oligarchic drift’ would undermine business confidence, reduce investment, degrade economic efficiency and punish success in ways unlikely to be good for the country or even to be appealing to most Americans,” they wrote.