To help pay for his big economic and social agenda, President Joe Biden is looking to go where the big money is: billionaires. Biden never endorsed an outright “wealth tax” when campaigning last year. But his more conventional proposed rate hikes on the income of large corporations and the wealthiest Americans have hit a roadblock. That leaves a special tax on the assets, not the income, of billionaires being proposed by a Senate Democrat as a possible vehicle to help pay for child care, universal pre-kindergarten, child tax credits, family leave and environmental initiatives. Biden has vowed that his programs will not add a penny to the deficit, which means selling to Congress and voters a tax on the wealthiest .0005% of Americans.