Ms. Warren is making the case that the economy could benefit if money is redistributed from the rich and corporations to uses that she and other liberals say would be more productive. Their argument combines hard data showing that high levels of inequality and wealth concentration weigh down economic growth with a belief that well-targeted government spending can encourage more Americans to work, invest and build skills that would make them more productive.

Fueling their argument is the fact that the United States now has one of the lowest corporate tax burdens among developed nations — a direct result of President Trump’s 2017 tax cuts. Tax revenues at all levels of government in the United States fell to 24.3 percent of the economy last year, the Organization for Economic Cooperation and Development reported on Thursday, down from 26.8 percent in 2017. America is now has the fourth lowest tax burden in all of the O.E.C.D., just above Mexico, Chile and Ireland, a development that Democrats say has helped corporate executives and shareholders get rich but has done little to help working Americans.

In making their pitch, Democrats cite evidence that transferring money to poor and middle-class individuals would increase consumer spending because they spend a larger share of their incomes than wealthy Americans, who tend to save and invest.

“The economy has changed, our understanding of it has changed, and we understand the constricting effects of inequality” on growth, said Heather Boushey, the president of the Washington Center for Equitable Growth, a think tank focused on inequality.

Inequality has widened significantly in America over the last several decades. The Congressional Budget Office estimates that the incomes of the top 1 percent of Americans more than tripled from 1979 to 2016, before taxes and government transfer payments are taken into account. For the middle class, incomes grew 33 percent. More than a decade after the recession, wage growth for the middle class continues to run well behind previous times of economic expansion, like the late 1990s.

Research by the economist Emmanuel Saez and colleagues shows that the last time such a small sliver of Americans controlled such a large share of the nation’s income and wealth was in the late 1920s, just before a stock market crash set off the Great Depression. World Bank researchers have warned that high levels of inequality are stifling growth in South Africa, which has the globe’s worst measured inequality.