In this letter, he states:
health insurance co-ops are not a real alternative to private health insurance and they are not a substitute for a strong public plan option, and we should not suggest to the American people that they would be.
Sen. Rockefeller did research on the history of coops and the applicability to the heath insurance field. He wrote letters to the National Cooperative Business Association (NCBA), the United States Department of Agriculture (USDA), and the Government Accounting Office (GAO) requesting detailed information about the current role of insurance coops in the heath care field.
In his letter to Baucus and Grassley, he describes what he found out as "astounding."
Read it all at Daily Kos