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Medicare for All remains the most contentious and consequential issue for 2020 Democrats. It’s easy to see why. A large majority of Democrats—and a slimmer majority of Independents—have said they approve of it. But even larger majorities of Democrats and Independents also want to keep their private coverage or enroll in a public program. Then there’s the cost: A recent poll of 3,000 Democrats in Michigan found that only 18 percent of single-payer supporters would be willing to pay as much as 10 percent more taxes for Medicare for All.

Elizabeth Warren says she can cover all or most of the costs with new types of taxes of individual wealth and corporations, but no one knows how those taxes will work until they’re tried. Bernie Sanders hasn’t shared any specific plans to pay for his proposal. Instead, he’s promised that the super wealthy will bear most of the burden and the benefits for middle-class Americans will outweigh some modest, if unavoidable, tax increases.

We can test Senator Sanders’s proposition by determining how much revenues Congress could raise by dramatically raising current taxes on wealthy people, corporations, and middle-class families. The results show that tax hikes on corporations and rich Americans would cover less than one-quarter of MFA’s expected costs. Moreover, even large tax increases on everyone (i.e. 50 percent hikes on income and payroll taxes) simply won’t be enough to fund what Sanders has promised.

According to the Urban Institute, the Sanders plan would cost $40 trillion over 10 years (2022-2031). A more conservative estimate by the Mercatus Center at George Mason University sets the 10-year cost at $32 trillion. The challenge, then, is how to cover costs averaging $3.2 trillion to $4.0 trillion per-year. But here’s the hitch: It doesn’t matter whether we define the wealthy as the top 0.1 percent, the top 1 percent, or even the top 5 percent of Americans. Hiking their income taxes by 50 percent would cover, at most, a small fraction of MFA’s costs.

Those calculations start with the most recent Internal Revenue Service data (2016), adjusted for increases in income since then. On this basis, the top 0.1 percent of taxpayers will pay $310 billion in income taxes in 2020. Increasing their income tax burden 50 percent would raise an additional $155 billion, which is less than four or five percent of MFA’s average annual cost. (For an account of how these and other estimates were derived, see this underlying study.)

If you expand the definition of the wealthy to include the top 1 percent, a 50 percent hike in their income taxes would raise $312 billion in 2020. Ease up more to cover the top 5 percent of taxpayers—everyone earning $250,000 or more a year—and the 50 percent tax increase would raise $489 billion in 2020. Those revenues cover 12 or 15 percent of MFA’s annual cost.

Sanders also calls for new taxes on corporations. The Congressional Budget Office (CBO) estimates that corporations will pay $245 billion in federal income taxes in 2020, so if Congress doubled the revenues from corporate taxes, it would raise at most another $245 billion. Add that to the new funds from a 50 percent tax hike for the top five percent of Americans, and this approach could bring in, at most, $734 billion in 2020—sufficient to cover at most 23 percent of MFA’s average annual cost.

The difficulty lies in the sheer scale of the challenge. Under current law, Medicare will cover 62.1 million people in 2020. MFA would add the 196.3 million Americans now privately insured and another 31.4 million people without public or private group coverage. Sanders has to find a way to pay for adding 228 million people to the Medicare rolls.

Dramatic increases in everyone’s taxes aren’t enough. Based on CBO revenue projections, adjusted for the 2022 to 2031 timeframe used by the Urban Institute and the Mercatus Center, the Treasury will collect an average of $1,668 billion per-year in payroll taxes, $2,597 billion per-year in personal income taxes, and $395 billion per-year in corporate taxes over that period.

So, if Congress raised everybody’s income and payroll taxes by 50 percent and doubled the federal corporate tax, it would raise $2,378 billion per-year over the next decade. That would only cover about 60 percent or 74 percent of MFA’s costs.

This funding challenge is even worse, because these revenue estimates are unrealistically high. They do not take account of how much higher payroll taxes could dampen employment and wages. They do not consider how much higher income and payroll taxes could reduce the incentive to work among part-time workers. The estimates also ignore the prospect that many large American companies could shift more of their operations to lower-tax countries when faced with a doubling of U.S. corporate taxes,

The idea of Medicare for All has powerful appeal. It promises to both achieve universal coverage and provide truly equal healthcare to everyone. But its reality carries an equally powerful cost: Paying for it would crush most taxpayers and businesses, and overwhelm the U.S. tax system. Sad to say, it’s a policy equivalent of the Venus Flytrap, drawing people in and then eating them alive financially.