Public health shouldn’t be contentious. But it’s incredibly polarizing.

The more aware we are of health issues, the more partisan we grow in our thinking about them.

On its surface, public health doesn’t seem as if it would be all that contentious. Who wouldn’t want to prevent disease or live a longer, healthier life?

But Republicans and Democrats couldn’t be more polarized these days in how they approach public health policy solutions.

Take, for instance, the current political furor over repealing and replacing the Affordable Care Act. Both parties say affordable health insurance for all Americans is essential, but they just couldn’t be more different in how to implement it or pay for it.

This kind of acrimonious debate over policy is the new normal in Congress — with the exception of the truly bipartisan effort to combat the growing opioid epidemic in the US (more on that later).

This is troubling because some of America’s most decisive health victories — widespread vaccination, fewer smoking-related deaths, fewer fatalities from car accidents — have all relied on bipartisan and often sweeping government legislation and intervention.

But the likelihood of passing bipartisan public health legislation is disappearing.

A recent paper from a pair of researchers at Drexel University found that in the past 15 years, Democratic senators were nearly 60 percent more likely to vote in favor of public health legislation endorsed by the American Public Health Association (APHA) than Republican senators.

On the Republican side, the fluctuation in support for public health bills can be explained by a couple of factors, said Jonathan Purtle, one of the study authors.

In the periods of 2006-2008 and 2011-2013, when a larger percentage of Republicans voted with APHA recommendations, it might have been because the bills were less polarizing or more clearly adhered to what we think of as traditional public health issues (as opposed to more politically charged issues like gun violence legislation or abortion protections), he said.

Or “it could be more about political dynamics and shifts — where things get particularly polarized and Republicans across the board vote no for everything,” said Purtle.

But Sarah Gollust, a professor of health policy at the University of Minnesota who studies how public opinion shapes public health, argues that the discrepancy in how Republicans and Democrats vote on public health is more fundamental. Public health is inherently “paternalistic,” she said, so almost all public health policy solutions have an underlying liberal bias.

“That the government has a role to play in improving the health of the public is in some ways baked into a public health mindset, and that is going to clash with those who don’t believe the government has a role to play in the health space,” said Gollust.

Public health issues rarely start out as politically divisive. But the more aware we are of the issues, the more partisan we grow in our thinking.

In the early 2000s, obesity was a growing epidemic in the US. Adult obesity had nearly doubled since 1980, and children with an unhealthy bodyweight had more than tripled.

Yet Americans weren’t all that concerned or interested in policies to fight obesity. Research found that most Americans thought people were obese because they lacked self-control.

But what stunned Eric Oliver of the University of Chicago and Taeku Lee of the University of California Berkeley was that a person’s political beliefs indicated “extraordinarily little” about how he or she thought of obesity.

In public opinion research, people’s political party — or whether they identify as liberal or conservative — is usually one of the most common lenses through which to understand how a person will view a particular issue.

But as late as 2001, political beliefs didn’t correlate to people’s understanding of obesity in the US. So Oliver and Lee were left wondering “whether obesity and weight-related issues are Democratic or Republican or whether they more closely align with liberal or conservative ideological views.”

Fast-forward eight years to 2009, and Americans’ views of how to treat obesity fell more or less along traditional party lines — liberals supported government intervention, while conservatives were resistant.

Why? Both Oliver and Sarah Gollust pointed to Michelle Obama’s efforts to combat obesity for politicizing the issue.

“In 2000, obesity wasn’t part of the public health agenda,” said Gollust. “But now, every survey that I've done related to obesity prevention [since 2009] shows polarization of viewpoints among the public. From the [former] first lady taking on [obesity] with ‘Let’s Move’ to more media coverage, there is an increase in the availability of political signals ... and we see partisan sorting.”

But targeted messaging can shift partisan views on health

Gollust was curious whether Americans’ willingness to support obesity prevention policies could be changed by rethinking how we frame obesity’s consequences.

She found that it could.

When presented with a prompt that said the military’s ability to protect the US was threatened by a growing number of young people too obese to serve (which is true), conservatives took obesity more seriously and were more likely to say they supported government-led obesity prevention policies.

What’s more, this prompt also shifted how conservatives thought about who was responsible for addressing obesity. Conservatives were more likely to shift the responsibility from individuals to third-party actors like the food and beverage industry and schools.

“We saw Republican support for obesity prevention policy and agreement that government should have a role go up and move closer to a level [of support] that Democrats had,” said Gollust.

She found liberals or Democrats were generally speaking more supportive of government-led public health interventions. So targeted messages about the different ways obesity impacts one’s health didn’t really change how liberals viewed obesity. In fact, when it came to messaging, liberals actually ranked the prompt about military fitness as one of the weakest reasons for government intervention.

But Gollust cautioned me that tailoring conversations around various health issues so that they appeal to just Democrats or Republicans won’t be enough to fix the current state of polarization. “Changing the way we frame issues will not be the silver bullet when the questions are as deep as who is deserving,” she said.

One health issue Republicans and Democrats aren’t divided on? Opioid abuse.

There is one health topic on which bipartisan consensus currently exists: opioid abuse.

In early 2014, researchers polled US adults on their thoughts about opioid abuse. They wanted to know if Americans thought it was a serious issue and what, if any, policy solutions they supported to combat it.

What they found surprised them. Americans on both sides of the political aisle not only thought opioid abuse was a serious problem, but of 16 possible policy solutions — ranging from stricter regulation of pharmaceutical companies to expanded Medicaid benefits — there was bipartisan support for all but two proposals.

The reason? People from both parties are equally likely to have known someone who has abused prescription painkillers.

The sobering reality, according to Robert Blendon, a professor at Harvard’s School of Public Health who has studied public opinion around opioids, is the opioid epidemic is so widespread in the US that it cuts across demographics and class divisions and even political party.

And even though certain areas of the country are harder hit than others (as you can see in the map below), researchers found that Democrats and Republicans are equally likely to consider opioid addiction to be a serious problem in their state.

People living in rural areas of the US are more likely to have known someone who abused opioids than people in urban areas. But “there is a high incidence of death from opioids in both white, rural Republican areas and low-income areas in cities,” said Blendon. And so urban Americans are just as likely as rural Americans to think that opioid addiction in the US is a serious problem.

What’s more, Blendon argues that the type of proposed government intervention around opioid abuse is particularly conducive to bipartisan support because it is limited in reach — no federally managed oversight, just policy solutions focused on bolstering existing state-run programs.

The Comprehensive Addiction and Recovery Act (CARA), which authorized $181 million annually to fight the opioid epidemic, passed in the summer of 2016 with almost unanimous support (94-1 in the Senate and 400-5 in the House).

“It’s a matter of both who’s affected by it and the nature of the government intervention,” said Blendon. “We’re not talking about 20 new federal laws, but rather state laws that will limit the ability of physicians to make certain types of prescriptions. It’s not the federal government running the opioid response.”

But researchers warn that if opioid addiction becomes politicized, or strongly associated with one of the two political parties, policy adoption will become more challenging.

“If this becomes an issue where politicians are competing for the best way to deal with opioids, we will see polarization emerge,” said Gollust. “But [the opioid epidemic] is also different in a lot of ways. It’s more common among white Americans, and that changes the questions about deservingness and groups.”

Some of the unhealthiest parts of America are also the most conservative — and the least likely to vote in favor of public health reform

In addition to finding that Republicans on the whole were less likely to vote in favor of public health legislation, Purtle and Goldstein also found in their paper that senators from the South were the least likely to vote for it.

“The South ... has some of the worst health outcomes and biggest racial disparities in terms of health,” said Purtle. “As one of the unhealthiest regions of the country, it has the most to gain, but it’s least likely to vote in favor of those policies.”

This is also true when you look at health insurance. As Vox’s Sarah Kliff found in her story on Obamacare enrollees in Kentucky, people who benefited the most from the Affordable Care Act still voted for Donald Trump, even though he has vowed to repeal it. (Many of them told her they voted for him because they didn’t think he would dismantle something so popular without making it better.)

Analysis from the Kaiser Family Foundation (KFF) has also shown that Republicans (many of whom live in the South) will be harder hit by an Obamacare repeal than Democrats living in bluer areas of the country like California and along the East Coast.

Of the 11.5 million marketplace enrollees, KFF found that 6.3 million live in Republican congressional districts, whereas 5.2 million live in Democratic districts.

But as Harvard’s Blendon told me, this makes sense ideologically.

Republicans or conservatives simply do not favor sweeping government intervention. And Blendon said public health “doesn’t get an exemption.”

As you can see in the chart below, 71 percent of Republican voters that Blendon and researchers polled before the election believed the federal government should have either a minor role or no role at all in the US health care system.

But most Democrats (87 percent) believed the opposite to be true and said the federal government should have a major role in the US health care system.

“The parties are further apart on domestic policy than they have been in the last 20 years,” said Blendon. “And there is a growing division between people who think government is a huge threat and apply it to every issue” and those who think the government should have more of a role in public health.

He thinks compromise will only be reached on matters of health care if states are given more authority on how they deal with public health legislation.

“You can get more conservatives on board if you say a state can have its own requirements for insurance and benefits,” Blendon said. “And if everything isn’t standardized by the federal government.”