With the 2020 presidential campaign in full swing, it is clear that the defining issue of the election will be economic inequality — and that puts America’s billionaires in the dock.

Proposals for a tax on extreme wealth have been put on the table by Democratic candidates Elizabeth Warren and Bernie Sanders, eliciting responses of varying vehemence from the billionaires lobby.

These responses, as we’ve reported, have been mostly negative, although here and there a few billionaires have allowed that, yes, they may have too much money and it might be good public policy to redistribute some of it through taxation.

The wealth tax proposals are part of a general attack on economic inequality that all the Democratic candidates share, to some extent.

“The middle class is getting killed,” former Vice President Joe Biden said during the Dec. 19 Democratic debate. “The middle class is getting crushed. And the working class has no way up as a consequence of that. The idea that we’re growing — we’re not growing. The wealthy, very wealthy, are growing. Ordinary people are not growing. They are not happy with where they are.”

Even the two certified billionaires in the Democratic race have expressed support for raising taxes on the ultra-wealthy. “I’ve been for a wealth tax for over a year,” Tom Steyer said during the debate. Michael R. Bloomberg, who did not appear at the debate, said at a campaign event in Phoenix three weeks ago that while a wealth tax of the variety proposed by Warren or Sanders “just doesn’t work,” he supports “taxing wealthy people like me.”

Sanders has proposed a graduated tax on net worth starting at 1 percent on wealth above $32 million for a married couple, rising in steps to 8 percent on wealth over $10 billion. The brackets are for married couples; for singles the thresholds would be halved.) Warren’s tax would begin at 2 percent a year on household net worth over $50 million, with an additional 4 percent surcharge on wealth over $1 billion.

Both proposals would raise trillions of dollars over a decade. Both are also designed explicitly to break up big family hoards. Sanders says that under his plan, “the wealth of billionaires would be cut in half over 15 years which would substantially break up the concentration of wealth and power of this small privileged class.”

And in the words of Emmanuel Saez and Gabriel Zucman, the UC Berkeley economists who are advisors to Warren on her wealth tax plan, “if the rich have to pay a percentage of their wealth in taxes each year, it makes it harder for them to maintain or grow their wealth.”

On the other side of the debate are commentators such as Erskine Bowles, a White House chief of staff under Bill Clinton, and Henry Paulson, a treasury secretary under George W. Bush, who called the wealth tax proposals “wishful thinking” in a recent op-ed and lumped it together with proposals such as universal health care (“Medicare for All”) as policies that are “fundamentally misguided and would result in economically harmful outcomes that could put our economy on an unstable and precarious path.”

Billionaires have been speaking for themselves, too. In October, money manager Leon Cooperman erupted to Politico about Warren’s plan: “This is the (blankety-blank) American dream she’s (blankety-blanking) on,” he said, using slightly more descriptive language.

A couple of weeks later, JPMorgan Chase Chairman and CEO Jamie Dimon (who is not a billionaire but travels in the same packs) groused on CNBC that Warren “uses some pretty harsh words — some would say vilifies successful people.”

For all their dudgeon, Cooperman and Dimon were rather more measured than the billionaire Silicon Valley venture investor Thomas Perkins, who in 2014 sought in a letter to the Wall Street Journal to “call attention to the parallels of fascist Nazi Germany to its war on its ‘one percent,’ namely its Jews, to the progressive war on the American one percent, namely the ‘rich.’”

It’s proper to note that more than 200 of the world’s wealthiest individuals and families have signed on to the “Giving Pledge” created by Bill Gates and Warren Buffett, a commitment to donate a majority of their wealth to philanthropy. The signers include Michele B. Chan and Patrick Soon-Shiong, the owner of The Times.

Whether such charity solves the social and economic problems of extreme wealth concentration is debatable, however, since the choice of how to distribute their wealth would remain in the hands of a small number of wealthy persons and underscores the issues raised by how their wealth became so concentrated in the first place.

Even a signer of the pledge has questioned whether it is accomplishing its goals. The pledge is growing “perhaps not as rapidly as we hoped,” stated telecommunications billionaire Leonard Tow in October.

Skepticism about the extreme wealth disparity isn’t a new phenomenon. Given the passage of time, and social and economic evolution, it’s difficult to pin down how the wealth inequality that has developed in this country compares to that of bygone eras and distant climes.

Pulitzer Prize-winning journalist Michael Hiltzik is a business columnist for the Los Angeles Times.