Biden says he supports taxing billionaires' investment gains annually

President Biden on Friday said he supports an idea championed by a key Senate Democrat to tax billionaires' unrealized investment gains annually.

Biden said the idea is one of a number of tax proposals he backs as ways to finance legislation that would advance his economic agenda. 

"I support a lot of these proposals. We don't need all of the things I support to pay for this, but I do support that," Biden said at the White House after giving a speech about COVID-19 vaccines.

Biden's comments come as congressional Democrats are working to determine how to pay for a $3.5 trillion social spending bill that includes many of the president's priorities in areas such as climate change and child care.

Senate Finance Committee Chairman Ron Wyden (D-Ore.) has been pushing for several years to tax wealthy people's investment gains annually, rather than when the investment gains are sold. He has recently been calling the idea a "billionaire's income tax."

"Instituting a Billionaire's Income Tax would go a long way toward creating one fair tax code, rather than one that's mandatory for working people and another that's optional for the fortunate few," Wyden said in a statement Thursday, after the White House released an analysis finding that the 400 wealthiest American families paid an average federal income tax rate of 8.2 percent from 2010 to 2018.

It remains to be seen whether Wyden's proposal will make it into a final piece of legislation agreed to by House and Senate Democrats and the White House. The proposal was not included in the legislation that the House Ways and Means Committee approved earlier this month.

When asked about the idea on Thursday, House Ways and Means Committee Chairman Richard Neal (D-Mass.) told reporters that staff members are talking about it but haven't reached any agreement.