Senate Democrats detailed their proposed levy on billionaires, a new and logistically risky approach to taxation that lawmakers hope will help fund President Joe Biden’s social spending aimed at low- and middle-income Americans.

The plan, sponsored by Senate Finance Committee Chairman Ron Wyden, is the result of weeks of negotiations among Democrats about how to find ways to raise taxes on the wealthy that nearly every member of the party can support. Wyden is betting that fellow lawmakers -- and voters -- will broadly back a plan that would shift more of the tax burden to the very wealthiest.