Musk, TIME's person of the year, became the world's richest man largely thanks to heavily subsidized industries: solar, space exploration and EVs.
The tax would have hit 700 billionaires like Elon Musk and Jeff Bezos, compelling them to pay a chunk of their wealth to the federal government.
The bottom 50% of the world holds 2% of wealth, while the top 10% holds 76%, according to a huge data set that leading economists compiled for years.
"The Senate has an opportunity to make this a truly historic piece of legislation," Sanders said in a statement after the House passed Biden's plan.
Democrats' idea of a billionaires' tax is "baloney," according to Leon Cooperman. He suggests closing loopholes and raising the income tax instead.
Musk said the government could "run out of money" and "come for you." Yet the government has run a deficit for years without billionaires paying much.
"I'm supporting basically that everyone should pay their fair share," Manchin said, allowing wiggle room. He represents a state with no billionaires.
A higher corporate tax, which Sinema reportedly opposed in recent weeks, would raise hundreds of billions needed for Biden's social spending plan.
Democrats' plan would tax the kind of on-paper capital gains that Musk, the world's richest person, made as Tesla hit a $1 trillion market value.
Democrats are eyeing alternatives after Kyrsten Sinema quashed an increased corporate tax rate. She and Manchin are huge influences over the plan.