"I don't care how low they drive support for this with misinformation," former President Bill Clinton said in August, referring to health care reform. "The minute the president signs this bill, his approval will go up. Within a year, when the good things begin to happen and the bad things they're saying will happen don't happen, approval will explode."

Clinton was speculating about President Obama's approval rating, not about views of health care reform itself. But he raises a timely question: If legislation passes, how might public opinion of the reform effort change?

Currently, though results vary, most surveys show slightly more opposition than support for the Democrats' plan. In the most recent NBC News/Wall Street Journal poll, 39 percent of Americans agree that "Barack Obama's health care plan" is a good idea, and 41 percent say it's a bad idea.

For more on public perceptions of health reforms, see Pollster.com.

We can get a hint of where those numbers might go from the extensive survey data collected by the Kaiser Family Foundation in the two years following enactment of the prescription drug benefit in Medicare, now known as Medicare Part D. One big lesson: The timing -- how long Americans have to wait until they feel benefits or pain -- will matter a lot.

Before Congress passed a prescription drug benefit in Medicare, Americans expressed overwhelming support for the idea. Between 1994 and 2002, Kaiser Foundation surveys showed 80 percent or more of adults favoring "a proposal to guarantee prescription drug coverage to everyone in Medicare."

The law that Congress ultimately passed, however, required seniors to buy private insurance to cover prescription drugs -- something that Kaiser surveys showed would be less popular than having Medicare provide the benefit directly. That decision, and the unusual political coalition that supported the bill, helped create a lot of confusion and suspicion among seniors. When Kaiser conducted its first tracking survey in February 2004, three months after the new Medicare drug benefit had passed, more than half of seniors (55 percent) had an unfavorable impression, and only 17 percent were favorable.

Over the next two years, Kaiser tracked continuing suspicion among seniors. More seniors rated the new law unfavorably than favorably on 10 of 11 surveys conducted through April 2006. Negative impressions dipped slightly in late 2005, shortly after the government began a marketing campaign but before seniors began making their choices and signing up for plans.

As our chart shows, the Kaiser surveys detected skepticism in late 2005 and early 2006 as enrollment began and seniors complained that the process was too complicated and confusing. Additional questions showed that media coverage in this period was more important in shaping these impressions than first-hand experiences with the program.

Once enrollment ramped up, however, and seniors began to gain actual experience with the program's benefits, their views grew increasingly positive. By November 2006, the last time the Kaiser surveys asked the question, more seniors rated the benefit favorably (42 percent) than unfavorably (34 percent). Moreover, a majority of seniors enrolled in the plan rated it favorably (54 percent), compared to only a third of those who had not enrolled.

More recent polling confirms the positive experiences seniors have had with the program. An AARP survey of enrolled seniors conducted in November 2008 found two-thirds (67 percent) either extremely satisfied or very satisfied, and only 13 percent not very satisfied or not at all satisfied with their Medicare drug benefit.

So what does this experience tell us about how Americans might react should a health care reform bill pass this year?

I put that question to Bob Blendon, the Harvard professor of health policy and political analysis who has studied Kaiser's prescription drug survey data. "If you give benefits out right away," he said, "and the benefits affect a lot of people, then all of the things President Clinton said are going to happen -- there will be support and people will like the bill."

The opposite scenario, Blendon warned, would be a repeat of the debacle that was the Medicare Catastrophic Coverage Act of 1988, a measure that would have "collected the taxes first, and people didn't get the benefits until two years later." The intense backlash against the bill led to its quick repeal after the unforgettable image of a group of angry seniors chasing down a fleeing House Ways and Means Chairman Dan Rostenkowski, D-Ill.

So what about the current bills, including the Senate Finance bill, now moving to floor votes in Congress? The most significant benefits, including the new coverage mechanisms and changes in insurance regulation, are not scheduled to take effect until 2013. However, the bill also includes some provisions that will launch in 2010, including a high-risk pool to help provide affordable coverage to those denied it due to pre-existing conditions and prescription drug discounts for seniors to cover gaps in Medicare Part D. It also includes some tax credits for small businesses that provide health insurance to their employees that will begin in 2011 and 2012.

So, should a bill pass, what aspects of the promised reforms will have the most influence in shaping impressions over the next four years, including the elections in 2010 and 2012? Will those currently without insurance react negatively as they learn about the costs of their soon-to-be mandated coverage? Or will the promised benefits -- and the pool to enable coverage to those with pre-existing conditions -- outweigh the costs? Will seniors react negatively to the proposed reductions in subsidies to Medicare Advantage that some argue will lead to benefit reductions, or will seniors be more impressed by the new drug discounts? How will businesses, large and small, react to the pending changes?

One thing is certain, according to Blendon: "The longer the gap between [enacting] a law and people getting instant benefits, the more you can raise uncertainties about it."