“When you say I should pay $100 billion, OK, then I’m starting to do a little bit of math about what I have left over,” he said at a New York Times Dealbook event. Warren responded to Gates on Twitter, saying she like to explain to him how the tax works and “promises” he wouldn’t pay $100 billion.

The congressional Democrats’ plans don’t raise anywhere near the $3.75 trillion over a decade that Warren estimates her wealth tax would bring to the Treasury.

Democrats could combine several of their ideas to match that total. For example, they could couple the surtax -- estimated to raise $635 billion -- with Wyden’s proposal -- estimated to raise $2 trillion -- with other ideas popular among Democrats.

Several bills to tax financial trades of stocks, bonds and derivatives have been introduced in the House and Senate, which could yield $777 billion over a decade.

Raising the top individual income tax rate to 39.6%, the rate before the 2017 Republican tax cut, generates another $111 billion. All told, that’s about $3.5 trillion in new tax revenue from wealthy taxpayers, without the implementation problems or court challenges that worry them about Warren’s approach.

Taxing wealth is a new approach to address inequality and raise revenue because the super wealthy don’t earn their income through paychecks, but from investments.

Warren Buffett, for example, is worth $87.5 billion, according to the Bloomberg Billionaires Index. But his 2015 tax returns show he only earned $11.6 million in income and paid about $1.8 million in federal income tax.

Patriotic Millionaires, a group that advocates for higher taxes on the wealthy, hosted an event on Wednesday to discuss a more progressive tax system.

Chuck Collins, a member of the Patriotic Millionaires and an heir to the Oscar Mayer fortune, said he supports an income surtax plan and called it a “plutocracy prevention program.”

“You’ve heard the discussion of the wealth tax — the wealth tax is a critical part, but it’s going to require a whole new regime,” Collins said. “This is a tax proposal that’s laser focused.”