Reasons for the Exceptional Nature of the American Welfare State

This is the first of my three (the next one is due sunday, and no, I have not started writing yet) long essays this semester and, nomen est omen, it deals with the reasons for American exceptionalism in public policy. Why does the US spend so much less on welfare than most European states (15% of GDP compared to around 25%), why is it less universalistic, why did it arrive so late? The paper is about 12 pages long and I do not like the end, think it sucks actually, but I do not have the time to rewrite it, so there you go.