In short, I'm doing a research project on the subject above. I'm in the preliminary stages of research but my intended focus is largely on the impact the American Progressive movement had in the early twentieth century on the emergence of the American welfare state under FDR in the 1930s.
Are there any primary and secondary sources my fellow (and likely more veteran in this particular field) historians would recommend I check out in this line of research?
I gave the same answer to a different question recently, but you should check out: Beyond the Bonus March and GI Bill: How Veteran Politics Shaped the New Deal Era, by Stephen R. Ortiz.
You might also want to look into the pensions given out to Civil War veterans. It was a pretty massive program and was arguably a precursor to the modern social safety net.