These conditions make it at once utterly remarkable, and totally explicable, that Mr. Sanders, the junior senator from Vermont and a democratic socialist, has become the front-runner for the Democratic nomination — and that Ms. Warren’s debate performance this week resonated as much as it did. You wouldn’t know it from watching cable news, where pundits are often aghast at the tastes of regular people who think green rooms are just rooms that are green, but in recent years, anger at billionaires has risen to a boil. This is thanks to the financial crisis, to endless wars cheered on by corporate and media elites and to yawning inequality. There is a growing sense that billionaires are not people who just happen to have drifted up from our midst, that in fact they are up there because they are standing on our backs, pinning us down.

Mr. Sanders and Ms. Warren, the senior senator from Massachusetts, have some meaningful differences of policy and personality. But the thread that connects their campaigns is their insistence that the “left behind” in America are not actually being left behind so much as stood on. They each seek to take the passive voice out of the grammar of American hardship: Your health insurance hasn’t somehow, mysteriously been made too expensive; your brick-and-mortar store hasn’t somehow, mysteriously been undercut. Someone did those things to you, probably by rigging the system to secure an undeserved advantage. And that person was probably a billionaire.

The degree of support for these ideas in 2020 is astonishing in a center-right country where, as John Steinbeck once wrote, explaining socialism’s limited growth in America: “We didn’t have any self-admitted proletarians. Everyone was a temporarily embarrassed capitalist.” It is a reflection of how fed up many Americans are with the old narratives about how, with a little pluck and patience, they too will rise. And it is a sign of a generational changing of the guard. As the (millennial) journalist Charlotte Alter, author of the new book “The Ones We’ve Been Waiting For,” told me, “Socialism is a generational Rorschach test: Boomers think of Soviet gulags and bad shoes, millennials think of Swedish health care and free education.”

In the mainstream of the Democratic Party, it has long been said that billionaires should pay more of their “fair share.” But, until recently, few would have questioned that you’d want more billionaires on the Forbes list, not fewer. Today a vocal chunk of the Democratic electorate is gravitating to a strikingly different conclusion: that America would actually be better off reducing its billionaire population through taxes and profit-trimming regulations.

(In fact, if I could ask one debate question, it would be this: Raise your hand if you would want there to be more billionaires at the end of your presidency than the start; raise your hand if you’d want fewer billionaires. Then, same question, but applied to millionaires. I think it would be revealing.)

Ballooning anti-billionaire sentiment is galvanizing billionaires. Some have been motivated to go on television to cast their critics as naïve and un-American. Others donate to centrist candidates like Mr. Biden, Mr. Buttigieg and Senator Amy Klobuchar of Minnesota, who serve a cocktail of down-home incrementalism shaken with wealth defense. But it took a special billionaire — Mr. Bloomberg, the former mayor of New York — to find a more direct way to thwart ascendant progressives. He is seeking to buy the election.

Just when the accountants thought they knew every tax-avoidance trick, here is the ultimate: become the leader of the free world. Of course, Mr. Bloomberg would say that he is running for an entirely different reason, which also happens to be very billionairey: He thinks he’s the only one with the wits and war chest to pull it off. “I alone can fix it,” as Mr. Trump once put it. It is something of a mantra for the billionaires.