The Congressional Research Service (CRS) is an agency within the Library of Congress that performs research for members of Congress.
Below is a sampling of CRS reports relating to SSI, Medicaid, and SNAP:
SSI
Medicaid
SNAP
Many CRS reports are not available online. Sources for publically-available CRS reports include: databases and commercial publishers. In addition, Congressional representatives will often provide copies of certain reports on request.
Below are links to sources offering CRS reports: