David Crowley, the Democratic nominee for governor of Wisconsin, vowed in a debate last week to make sure “that those who are making enough money pay their fair share.”How much is “enough money”? How does he define “fair share”? He didn’t specify. He probably has a different assessment than many voters.

Wealth and fairness are in the eye of the tax assessor, which is something to keep in mind as Democrats campaign to make the “rich” pay their “fair share.”They may rail against billionaires, but Joe the HVAC repairman, not Elon the trillionaire, is their real target.

Economists Owen Zidar and Eric Zwick make this clear in their book, “The Everywhere Millionaire.”They note that most of the nation’s wealth is concentrated among small-business owners. In their view, auto dealers, fast-food franchise owners and plumbers are the primary cause of inequality in America, and they aren’t paying anywhere near their fair share in tax.

By the authors’ calculation, there are three million “Main Street millionaires” who own private businesses and have a net worth of at least $5 million: “Collectively, Main Street Millionaires have more than thirteen times the wealth of the Forbes 400. For every member of the Forbes 400, more than four thousand private business owners each have at least $10 million in net worth.”

“For every large public company CEO, more than one thousand private business owners have at least $25 million in wealth,” they write. “Far more than a few high-profile billionaires on the coasts, these are the real rich in America.”If you built a successful small business by the sweat of your brow, congratulations—you’re rich. Now fork it over. As Messrs. Zidar and Zwick tell it, owning a small business “is the best tax deal in America.”They gripe that Main Street millionaires use their political clout to promote lower taxes that help them expand their businesses and—oh no—accumulate wealth.

“No battle better illustrates Main Street Millionaires’ political influence,” they write, “than their long and successful campaign to eviscerate the estate tax.”The Tax Cuts and Jobs Act of 2017 doubled the federal estate tax exemption to $11.2 million per decedent and adjusted the amount annually for inflation. Republicans last year made permanent the larger exemption (now $15 million, or $30 million for married couples). Assets exceeding the exemption are taxed at 40% before the estate is distributed to heirs.

The larger exemption is an acknowledgment that the estate tax punishes investment and saving. If you listen to Democrats—or for that matter, to United Airlines CEO Scott Kirby—punishment is the point.

In their view, too many so-called rich are dodging taxes by investing their hard-earned money and leaving the bounty to their kin. Mr. Kirby last week said he favored “inheritance taxes that get close to 100% at some level.”“If you’re wealthy enough, you can have passive income, you can just make an investment, and the laws are set up that you literally never pay taxes on all that growth that can happen,” he told Bloomberg News. “And that just feels unfair to me.”That’s easy for him to say. High-flying CEOs and billionaires have the means to hire accountants and lawyers to help them dodge death and income taxes—and potential wealth taxes. Less so small-business owners.

Because targeting Main Street businesses isn’t popular, Democrats instead lambaste billionaires. See California’s Proposition 40, which seeks to impose a 5% tax on the fortunes of residents with more than $1 billion in net worth. French economist Emmanuel Saez, one of the initiative’s architects, recently explained to the New York Times that targeting only billionaires was a strategic choice, since they “are no longer very popular.”In 2020, Mr. Saez helped 14 California Democratic lawmakers, including now-Attorney General Rob Bonta, craft a bill to impose a 0.4% wealth tax on taxpayers with more than $30 million in assets.

It foundered amid opposition from Gov. Gavin Newsom, but if Proposition 40 passes, don’t be surprised if wealth tax proponents later seek to lower the threshold.

New York City Mayor Zohran Mamdani names and shames billionaires like Citadel CEO Ken Griffin. This is a head-fake. His proposed tax hikes would primarily whack owners of local bodegas, plumbing companies and other small businesses. So, too, “millionaire taxes” popping up in states across the country.

Abdul El-Sayed, Michigan’s Democratic nominee for U.S. Senate, advocates imposing an additional death tax by requiring heirs to pay income tax on inheritances worth more than $1 million. Some 24 million Americans could get soaked, most of whom are solidly middle-class. He also wants to remove the $184,500 earnings cap on the 12.4% Social Security payroll tax “to make sure the rich pay their fair share.”If you earn more than $184,500, you are rich. Congratulations. Progressives don’t merely want to redistribute wealth. They want to raise taxes to aggrandize their own power and level opponents. Then they can decide what’s fair and who has enough.