Four years ago, after a hard-fought election campaign, a president tried to use his newly won mandate to reform a program that touched every American family: Social Security.

President George W. Bush soon discovered that his mandate wasn't nearly as powerful as he thought. Even though Bush promised that current pensioners' benefits wouldn't be cut, senior citizens were nervous about any change. In effect, they told the federal government to keep its hands off their Social Security. Bush stumped the country explaining and defending his proposals; they died without Congress ever taking a vote.

President Obama has run into much the same problem with health care reform. Public backing for Obama's ideas has been broad but tepid; it's difficult to rally support when the president hasn't said exactly what he's seeking. Meanwhile, a small but vocal opposition has been ferocious — and it includes not only hard-core Obama-haters but also a significant number of senior citizens, the nation's most powerful voting bloc.

In public opinion polls, young people generally support Obama's proposals, but people older than 65 do not. That generation gap mirrors last year's election returns: Senior citizens were the only age group Obama didn't win. But it also reflects fear among the elderly that Obama's drive to make Medicare more cost-efficient could eventually limit their medical choices — as indeed, it probably would.

The skittishness of older voters was only one of several danger signs for Obama in polls taken after the Republicans' summer offensive against his health care proposals. An NBC poll found that more people now think Obama's proposals are a bad idea than a good idea, 42 percent to 36 percent. The same poll found that 55 percent believed that Obama's proposals were likely to provide health insurance to illegal immigrants (they won't).

Still, despite all that bad news for Obama, there are several ways his health care venture is different from Bush's 2005 attempt to remake Social Security — contrasts that suggest how he can still succeed where Bush failed.

One is contained in that poll question about illegal immigrants: Some of the opposition to "Obama-care" stems from the wild misinformation his opponents have spread. The administration has slowly succeeded in rebutting Sarah Palin's charge that its plan calls for "death panels"; given time, it can handle the other whoppers as well.

A second strength Obama holds is his ability, often displayed in last year's campaign, to improve his sales pitch over time. In his most recent town hall meetings, Obama emphasized a new, more family-friendly (and less ambitious) message: consumer protection for the middle class. If you already have an insurance policy, he said, his plan will make sure your coverage won't be canceled when you need it.

Finally, the most important difference between Obama's health care proposals and Bush's Social Security idea is this: Obama has left himself plenty of room to downsize his plan. Too many voters think end-of-life counseling sounds like a "death panel"? Out it goes. That ambiguity has been frustrating, but it has left Obama in a position where he's still likely to get some kind of health care reform through Congress. Even if it's less ambitious than he once wanted, he will still be able to claim a victory.

"Health reform has survived the August town-meeting wars with just enough public support to move forward," said Drew Altman, president of the Kaiser Family Foundation.

"The critical question for most people is: What is this going to do for me and my family, and is there something here I'm afraid of?"

Those are the questions that will determine the outcome of the battle once Congress returns to Washington on Sept. 8. The fight that starts then will make August's town meetings look like a sideshow.

Doyle McManus is a columnist for the Los Angeles Times.