“They’re not paying their fair share,” said one Democrat, Fred Wood, a retired teacher in Williamsport, Pa. “It’s just not right when folks cannot afford health care.”

Polling support is by no means a guarantee that Americans would elect a tax-the-rich challenger to President Trump — who mused as a candidate about raising taxes on the rich but as president signed a $1.5 trillion tax cut that reduced the top marginal income tax rate and primarily benefits high earners. Polls by Gallup and other organizations over the decades have regularly found that a majority of Americans believe that corporations and the wealthy pay too little in taxes, but voters have frequently elected presidents who cut those taxes, instead.

What appears different this time, analysts say, is the emphasis that leading Democratic candidates are placing on taxing the rich. “This is about politicians catching up to where Americans have been,” said Leslie McCall, a political scientist at the CUNY Graduate Center.

As a result, progressive policy hands say they are increasingly confident that if a Democrat wins the White House and the party gains full control of Congress, taxes on the rich will go up. That is partly because of the “finally dawning realization among Democrats that taxing the rich is good politics along with good policy,” said Michael Linden, a fellow at the liberal Roosevelt Institute.

“My bet is that it won't be one big thing” that ends up raising taxes on the rich, Mr. Linden said. “I bet it will be a lot of medium-sized things. A higher top rate, for sure. Rooting out or limiting some of the tax expenditures that disproportionately benefit the rich. I think the corporate rate will start to creep back up. And I think new taxes like a wealth tax, or some other form of capital taxation, are very likely.”