The first and second Democratic debates have made one thing clear: A number of major policy reforms are on the table, including sweeping proposals on health care and climate change. And many of these ideas appear popular among the majority of Americans. A July Marist poll found that 63 percent of Americans said a plan like the “Green New Deal,” which would address climate change by investing heavily in environmentally friendly jobs and infrastructure, was a good idea; similarly, 70 percent said they supported “Medicare for all who want it,” which would give Americans a choice between government-sponsored health insurance and private insurance.

But beneath those top-line numbers are red flags about just how much the popularity of these reforms depends on how they are written and enacted. That same Marist poll found, for instance, that most Americans do not think “Medicare for All” is a good idea if it means replacing all private health insurance with the government version. This is important to keep in mind as public opinion toward a complex policy can be dictated by the plan’s least-popular element.

Let’s take the Affordable Care Act as an example. Just before Barack Obama’s inauguration in 2009, 51 percent of Americans in an Associated Press poll said “implementing a national health care plan” was a top priority. And early in Obama’s presidency, the majority of Americans surveyed in a 2009 CNN poll approved of the job he was doing on health care. But once the law passed in 2010, it was generally rated unfavorably until President Trump took office and the prospect that the law would be scrapped became real.

For many commentators and advocates of the health care law, this was surprising. I wrote in 2010 that it wasn’t that health care reform was unpopular, but rather the political debate was turning people off — and I figured that once the law passed, public opinion might shift in the ACA’s favor. After all, it’s a complex law with a wide variety of provisions, including an expansion of Medicaid and protections for people with pre-existing conditions, plus smaller items that might have flown under the radar, like reducing tax breaks on insurance company executives’ pay and adding support for seniors’ prescription drug payments.

Many of the law’s individual provisions were quite popular. According to a Kaiser Family Foundation poll from December 2014, around three-quarters of Americans favored the ACA’s creation of insurance exchanges, the law’s subsidies for lower-income Americans’ insurance costs and the Medicaid expansion. Sixty percent even supported the law’s mandate that employers with at least 100 employees pay a fine if they didn’t offer health insurance. However, that pattern didn’t hold for one key element of the ACA, the individual mandate. It required all Americans to have health insurance or pay a fine. The mandate has consistently polled poorly, with just 35 percent saying they supported it in that 2014 KFF survey.

People liked most ACA provisions … with one exception Share of Americans who had a favorable opinion of each provision in the Affordable Care Act, according to a 2014 poll Dem. Rep. Ind. Total Create exchanges/marketplaces 91% 66% 79% 78% Subsidy assistance to individuals 90 55 78 76 Medicaid expansion 90 52 78 75 Large employer mandate/penalty 78 34 61 60 Individual mandate/penalty 53 17 31 35 2014 numbers are used because the ACA became significantly more popular after President Trump took office and the chances of repealing the law increased. Source: Kaiser Family Foundation

Still, if Americans’ overall attitudes toward the ACA were a weighted average of their views on its individual parts, the ACA should have been popular. But that clearly wasn’t the case: In that KFF survey, 41 percent had a favorable view of the law overall compared with 46 percent who had an unfavorable view. In other words, Americans’ opinion of the law overall were quite close to their opinion of the individual mandate, its least-popular provision.

And that may be in part because of the law’s many provisions, only a few have gotten sustained public attention, including some of the law’s more unpopular features. In a March 2017 KFF survey, 82 percent of Americans said they knew about the individual mandate while 69 percent said they knew about the subsidies for low-income Americans and 65 percent said they knew about the Medicaid expansion.

To better understand what Americans knew about other aspects of the law, Cornell University’s Will Hobbs and I conducted an online survey in the fall of 2018 where we asked respondents whether a variety of policies were included in the original ACA. This survey wasn’t representative — respondents were not randomly selected from the general population, and instead opted to take an online survey.

A majority of respondents were only able to recognize four of the main elements of the ACA: the individual mandate, the provision allowing young adults to remain on their parents’ insurance until age 26, the creation of the health insurance exchanges to buy insurance, and protections for pre-existing conditions. Only 34 percent knew that the ACA involved substantial taxes for people in upper income brackets, and only 29 percent knew that it had closed the loophole in Medicare prescription drug coverage. Even fewer (17 percent) knew that it included a provision to limit the tax breaks companies received on salaries paid to insurance company executives.

So what does this mean for major policy proposals like Medicare for All or the Green New Deal? Well, the ACA provides a cautionary tale. Initial polling about major initiatives can be misleading. And even if most elements of a policy poll well, public opinion may come to be driven by the policy’s least-popular items. That’s especially true if the opposition launches an extended campaign against it.

The ACA also highlights an important difference between how policymakers and the public think about a complex policy. For the ACA’s architects, the legislation was an integrated whole, with various provisions working in tandem to increase access to comprehensive insurance. The individual mandate, for example, was thought to be critical to driving younger, healthier people to buy insurance and to keep overall costs down. But when making sense of that same policy, citizens focused on just a few of its most salient — and controversial — elements. In other words, when it comes to public opinion, the ACA made it clear that the whole is often not the sum of its parts — and that could spell trouble for other big policy proposals.

The Russell Sage Foundation provided funding for some of the research described here.