FDR needed more revenue to support his big-government schemes. More importantly, he needed a villain to explain why, given the passage of his New Deal legislation, government spending and regulations, the economy was still struggling.
So he proposed raising taxes on the rich, which he dubbed a “Wealth Tax.” As he explained to Congress in June 1935, “Our revenue laws have operated in many ways to the unfair advantage of the few, and they have done little to prevent the unjust concentration of wealth and economic power. … Social unrest and a deepening sense of unfairness are dangers to our national life which we must minimize by rigorous methods.” President Obama couldn’t have said it better himself.
Obama: Campaigning Like It's 1936 - Forbes