Social Security enshrined ideas ranging from unemployment compensation and aid to dependent children to the concept of social insurance for the elderly and other Americans as new social rights. It seems safe to assume that the current liberal opposition to a reform plan without a "public option" will diminish, provided final legislation covers all Americans. So it's conceivable that healthcare reform will establish the principle of universal healthcare coverage as a right for all Americans, also for the first time, after decades of struggle.
It's hard to exaggerate how significant such a development would be. While progressives understandably criticized Social Security in 1935 as flawed, they came to regard it as possibly the single greatest achievement of liberalism in the middle of the 20th century. Progressives one day may point to Obama's healthcare reform legislation—regardless of the contentious provisions under debate today—and cite it as the most important progressive action of the early 21st century.