Supporters say the candidates are reacting to voter frustration over sluggish wage growth and spiking costs across working families’ lives, including housing, child care, schools and health care, along with concerns about inaction toward climate change.

“I think people don’t care as much about taxes as they care about how their life is going,” said Betsey Stevenson, a University of Michigan economist who helped develop a list of possible tax increases and spending cuts that Ms. Warren drew on to fund her health care proposal.

“Our climate problems have only gotten worse,” she said. “Corporate greed has only gotten worse. We’ve continued to see the gains go disproportionately to the top. And we’ve continued to see the bottom 90 percent — it’s just not all working for them.”

Those concerns have been exacerbated by Mr. Trump’s economic policies, including a $1.5 trillion tax cut, which delivered its biggest gains to corporations and wealthy Americans, and has yet to produce the sustained investment boost and accelerated wage gains for middle-class workers that the administration promised.

In the decade-long recovery from the Great Recession, real incomes for the top 1 percent of American households have risen 38.5 percent, according to research by the economist Emmanuel Saez at the University of California, Berkeley. Incomes for the bottom 99 percent grew 10 percent over that same time frame.

Still, not every Democrat is embracing the type of aggressive redistribution that Ms. Warren and Mr. Sanders propose. Former Vice President Joseph R. Biden Jr. wants to reverse Mr. Trump’s tax cuts for corporations and the “super wealthy” and raise taxes on investment gains for multimillionaires. But he has criticized Medicare for all, proposing instead to expand Mr. Obama’s Affordable Care Act, in part by giving Americans the option to buy into a government health plan — all funded by increased tax rates on capital gains.

Representatives for Mr. Biden said Friday it was not possible for Ms. Warren to pay for her plan without raising middle-class taxes, a criticism she brushed off while speaking to reporters in Des Moines.