The top Democrat on the Senate Finance Committee, Ron Wyden, is reviving a plan that would tax wealthy individuals annually on their investments, instead of when those assets are sold.

The plan represents a fundamental change to the timing of capital gains taxation -- it would require wealthy investors to pay the capital gains tax on their assets each year, rather than paying the capital gains tax once when they sell an asset. The proposal, which is unlikely to become law while Republicans control the Senate and White House, is likely to be discussed by Democratic presidential hopefuls ahead of the 2020 elections.

“This eliminates serious loopholes that allow some to pay a lower rate than wage earners, to delay their taxes indefinitely, and in some cases, to avoid paying tax at all,” Wyden said in a statement Tuesday.

Wyden’s overhaul of the capital gains taxation system is frequently called “mark-to-market” taxation in policy circles. The Oregon Democrat has introduced similar proposals for several years and it was briefly discussed during the 2017 Republican tax overhaul, but ultimately was not included because of the complicated nature of how to structure such a plan.

Wyden’s proposal comes as the Democrats are envisioning new ways to tax the rich ahead of the 2020 presidential election. One hopeful, Senator Elizabeth Warren, has proposed an annual 2 percent wealth tax on households worth more than $50 million. Other contenders, including Senators Bernie Sanders and Kamala Harris, have backed expanding the estate tax as a way to pay for social programs.“Mark-to-market would certainly increase the tax liability on the wealthiest,” Kyle Pomerleau, an economist at the conservative Tax Foundation, said in an email.

And Steve Wamhoff, the director of federal tax policy at the left-leaning Institute on Taxation and Economic Policy, said the bill “would certainly slow down the ability of billionaires to accumulate massive fortunes very rapidly.”

Wyden said he would explain in the coming weeks how he plans to structure the tax.

This article provided by Bloomberg News.