Everything moves faster in today’s society, of course, and it probably won’t take 15 to 20 years for the politics of health care to cement itself. And yet there are essential lessons that both parties can draw from the history of Social Security and other expansive programs.

Republicans must know that they are effectively racing against time. The fact that much of the health care program remains to be phased in over the next several years states are just beginning, for example, to create their health care exchanges, which won’t be up and running until 2014  means that the best time to attack core elements of the law is right now. That’s because we’re in the window of time between passage and acceptance of the law, where the public remains skeptical of a giant new program and hasn’t yet grown accustomed to its benefits.

This is precisely what happened to the catastrophic-insurance program that a Democratic Congress and President Ronald Reagan added to Medicare 1988. Opponents in both parties succeeded in repealing the program within 18 months, as older Americans who hadn’t yet warmed to the entitlement railed against the higher costs. “There’s a case where the window was open, and the opposition slammed it shut,” says Byron Shafer, a political scientist at the University of Wisconsin.

Democrats were clearly mindful of that time window and the peril it posed to the new health care law, which is why they devised the program in such a way that the costs don’t really kick in until after the 2012 election. For them, the challenge now is to repel legal and political attacks on the program, at least in an existential way, until the public begins to make work and family decisions based on the new law. If that happens, history would indicate that conservatives might have to turn their attention to reforming the law, rather than repealing it outright.

Most consequential for Democrats, of course, is that Social Security and Medicare not only survived but remade the country’s political calculus as well, delivering working-class and older voters into the Democratic fold for decades. Liberals hope that health care might ultimately become the quintessential middle-class entitlement, something that enables them to say to today’s young voters, as Stevenson’s campaign did, “Democrats made it possible.”

It could happen. It’s just not happening anytime soon.