Almost as soon as it surfaced as a leading contender to finance the Biden administration’s ambitious spending plans, the so-called billionaire’s tax was laid to the side by Democratic politicians as they scramble for a lucrative revenue source.

That likely meant sighs of relief among the state’s billionaire class, particularly Morningstar Chairman Joe Mansueto and real estate mogul Sam Zell, whose fortunes rest substantially in publicly traded stocks. The billionaire levy would have applied immediately to the change in value of publicly traded assets like stocks, leaving hard-to-value assets untaxed until their sale.

Of the 22 Illinoisans on Forbes’ list of billionaires, a handful stand out in terms of stock-related wealth. In addition to Mansueto and Zell, they include Thomas Pritzker, executive chairman of Hyatt Hotels, and Patrick Ryan, founder of Aon and chairman and CEO of wholesale insurance brokerage Ryan Specialty Group.

The proposal, which Senate Democrats made public today, would have required billionaires to pay an annual tax on the rise in value of their assets. Current law doesn’t tax capital gains until the assets are sold; the measure would take the unprecedented step of taxing paper gains. It emerged this morning as a leading contender to help finance the reconciliation bill containing a host of Democratic spending priorities for child care and health care for seniors, among other things.

But pivotal Sen. Joe Manchin of West Virginia objected to it, and Democrats now are mulling a 3% surtax on the income of those making more than $10 million a year, Bloomberg reported.

Mansueto was perhaps the most exposed of the state’s billionaire class. He owns 45% of the shares of Morningstar, the mutual fund ratings firm he founded in the 1980s. That stake today is worth $5.9 billion. Forbes pegged Mansueto’s wealth at $5.2 billion in its most recent rankings, when Morningstar’s stock was lower.

The proposal would have required billionaires like Mansueto to pay a one-time levy on the gains in their publicly traded assets over the lives of those investments, although it would have allowed them to spread that payment over five years. His basis in Morningstar’s stock is likely to be low, given that he founded the company nearly four decades ago. A 20% tax on, say, $5 billion would have meant up to a $1 billion bill from the Internal Revenue Service.

After the one-time levy, billionaires would have had to pay each year on the gains in their publicly traded portfolios. Losses would have reduced the tax on future gains.

The idea behind the extraordinarily targeted tax was that the uber-wealthy have benefited far more from the U.S. economy over the past several decades than have ordinary people. The wealthy also avoid taxes, perfectly legally, by borrowing against their assets in order to generate tax-free income.

With U.S. Sen. Kyrsten Sinema, D-Ariz., reportedly opposed to raising tax rates on corporations and wealthy individuals, the billionaire’s tax had emerged as a leading alternative.

A spokesman for Mansueto didn’t respond to requests for comment on his exposure or the thinking behind the proposal.

He’s not the only local billionaire in the sites of the proposal. Sam Zell, whom Forbes pegged as the third-wealthiest Illinoisan after Citadel founder Ken Griffin and casino and real estate mogul Neil Bluhm, has a substantial amount of his estimated $5.3 billion tied up in publicly traded stocks.

Zell has large stakes in at least four publicly traded companies he chairs—Equity Residential, Equity LifeStyle Properties, Equity Commonwealth and Covanta Holding, according to proxy statements. Together, those holdings are valued now at $1.2 billion.

His basis in the stocks isn’t known. But a cumulative gain of, say, $800 million would have meant potentially a $160 million tax bill.

A spokeswoman for Zell declines to comment.

Thomas Pritzker, cousin of Gov. J.B. Pritzker, is another who may well have been on the phone to his accountant. Hyatt Hotels is the source of much of the famously wealthy family’s fortune. The publicly traded company has a dual-class share structure meant to retain family voting control even as their ownership share declines, which makes precisely valuing Thomas Pritzker’s stake a little complicated.

But the executive chairman of Hyatt holds a little over 22% of the company, according to the proxy statement. With Hyatt’s market value currently at $9.3 billion, that stake is valued now at about $2 billion.

A spokeswoman for Hyatt didn’t respond to requests for comment.

He isn’t the only member of the Pritzker clan potentially exposed. Former Commerce Secretary Penny Pritzker, Jennifer Pritzker and other family members all hold substantial stakes in Hyatt, according to a proxy statement. (Gov. J.B. Pritzker has no stake in Hyatt, a spokeswoman says.)

Patrick Ryan, minority owner of the Chicago Bears and leading benefactor of Northwestern University, took his Ryan Specialty Group Holdings public just a few months ago, which would have exposed him to a hefty tax bill if the billionaire’s tax moved forward. He owns more than 45% of the firm, which he founded in 2010, if his Class A and Class B shares are combined. (Like Hyatt, the firm’s ownership is divided into two share classes aimed at Ryan retaining voting control even as his percentage ownership declines over time.)

Of the Class A shares that trade on the open market, though, he owns a little over 11%. Ryan Specialty is valued currently at $4.1 billion, making that stake worth close to $450 million.

In addition, his remaining ownership in London-based Aon, the world’s second-largest retail insurance brokerage, is unknown. Ryan founded Aon and retired as chairman in 2008. His ownership stake was more than 6% in 2010, but he sold enough shares after that to fall below the 5% threshold for reporting.

Forbes pegged his fortune at $3.5 billion, but that was before the initial public offering for Ryan Specialty. It could be higher.

Ryan didn’t respond to requests for comment.

As for those on the list whose fortunes are tied to hard-to-value assets like privately held companies, real estate, sports teams and the like, they would have escaped immediate taxation on those gains. But, in recognition of the difficulty in valuing those holdings each year, the proposal would levy the tax upon their sale. The tax would have assessed an extra amount based on an estimate of interest on each year’s gain that was forgone by the government while the billionaire held the investment.

So, at some point in the future, the state’s wealthiest man, according to Forbes—Citadel founder and CEO Ken Griffin—would have had to pay. Just not now. Forbes valued his fortune at $16 billion.

Just behind him in the Forbes rankings is Chicagoan Lukas Walton, a philanthropist who is one of the heirs to the Walmart fortune. What portion of Walton’s wealth is in the form of tradable stocks isn’t public.

This story has been corrected to indicate Gov. J.B. Pritzker isn’t a shareholder in Hyatt Hotels.