WASHINGTON — When President Obama signed the health care bill into law last spring, White House aides predicted that the political benefit to their party would be almost immediate, going so far as to suggest that some provisions, like the one requiring insurance companies to cover pre-existing conditions, would help Democratic chances in the November elections....

The pattern here is perhaps best illustrated by Social Security. Franklin D. Roosevelt signed the program into law in 1935, but it didn’t begin to pay out benefits until 1941. It was attacked both by conservatives, who tried repeatedly to repeal it, and by some on the far left, who thought the program insufficiently generous, and its survival remained in doubt for more than a decade.

Even as the political maelstrom raged, though, Social Security was slowly expanded to cover more categories of workers, and a generation of retirees began receiving their checks. “It basically gets woven into the way employers are operating and people are planning,” says the political scientist Theda Skocpol, a Harvard professor who has written extensively on the history of American social policy. “People didn’t get used to the benefits to which they were entitled until the ’50s.”...