How big a lift is it to raise $32 trillion? It’s almost 50 percent more than the total revenue the CBO projects Washington will collect from the personal income tax over the next decade (about $23.3 trillion). It’s more than double the amount the CBO projects Washington will collect over the next decade from the payroll tax that funds Social Security and part of Medicare (about $15.4 trillion). A $32 trillion tax increase would represent just over two-thirds of the revenue the CBO projects the federal government will collect from all sources over the next decade (just over $46 trillion.)

Taxes that can fill that big of a hole are not easy to identify. Even by Warren’s own estimates, which some liberal economists consider too optimistic, her proposed wealth tax on personal fortunes exceeding $50 million would raise just $2.75 trillion over the next decade. That’s less than what would be required to fund a single-payer plan for one year. In any case, Warren has already targeted that revenue for other proposals she’s issued, such as providing universal preschool and child care, and canceling most college debt while funding tuition-free public higher education. Repealing the tax cuts for businesses and individuals that President Donald Trump and the GOP Congress passed in late 2017 would similarly raise about $2 trillion in federal revenue over the next decade.

Other tax options would likewise make a relatively minor dent. For instance, some Democrats have proposed for years to eliminate the current cap on the payroll tax—which stops taxing income above about $133,000—and instead impose the tax on all income above a higher threshold, such as $250,000. The CBO recently estimated that such a plan would raise about $1.2 trillion over the next decade, again a small share of single payer’s cost. Besides, Warren has already proposed such a tax hike and earmarked the money to increase Social Security benefits.