Hence my apology for the imprecise language. I meant what you said by social democracy, not a social economic system. Anyways, if we're being pedants, there are no true socialists or capitalists in today's markets. They're all mixed-market economies.
When I say socialist (and what is more accurately social democracy), I first think of healthcare, then I think of transit, then of education, and then of utilities. These are things that the US certainly could do better.