If the United States had implemented a moderate wealth tax in 1982, Jeff Bezos' fortune would be half what it was in 2018 and Bill Gates would be $61 billion less rich, a study published in the Brookings Papers on Economic Activity found.

America's inequality problem has become central to the Democratic primary; frontrunner Bernie Sanders lampooned former candidate Pete Buttigieg for accepting donations from billionaires and Mike Bloomberg for being one. Buttigieg suspended his campaign on Sunday, and Bloomberg did the same Wednesday after a disappointing showing on Super Tuesday. Joe Biden, another frontrunner, has said that he does not support a wealth tax.

The idea of taxing the net worths of Americans has gained traction in recent years, but proposals have been hampered by questions over the effectiveness and the constitutionality of such a tax, Business Insider previously reported. Elizabeth Warren was the first Democratic contender to propose a formal wealth tax, and Sanders soon followed with an even more aggressive plan.

The Brookings Study, "Progressive Wealth Taxation" by The University of California at Berkeley's Emmanuel Saez and Gabriel Zucman, concludes that "the wealth tax has great revenue and wealth equalizing potential in the US context."

How a wealth tax would work

A wealth tax would require that ultra-wealthy Americans pay the federal government a small percentage of their net worth each year.

One of the most frequently cited proposals, Elizabeth Warren's "Ultra-Millionaire Tax," calls for a 2% annual tax on households with a net worth between $50 million and $1 billion and a 3% annual tax on households with a net worth over $1 billion. Warren has since proposed increasing the tax on households with net worths over $1 billion to 6%, but has yet to modify the proposal on her campaign website.

The idea has support from ultra-wealthy and ordinary Americans alike: An Insider poll shows that more than half of Americans support Warren's wealth tax proposal.

Keep reading to see how rich America's richest billionaires would be if the country had a moderate wealth tax.