FDR was a social democrat and the reason his social policy didn't stick around is because he compromised with racists and allowed them to condition the passing of welfare policy on the exclusion of black and brown Americans from receiving any benefits, and he also did not sufficiently challenge the power of capitalist property owners. When the civil rights movement began to see success in forcing the universalization of social welfare the still-powerful capitalists were able to ride the wave of the racist backlash towards the near-total dismantling of the welfare state.