How does an HIV outbreak happen in rural Indiana? The deadly pandemic manifests in the United States mostly as an affliction of urban density, with a special affinity for low-income people of color. Rural Indiana doesn’t fit that description, and the state has managed infection rates well below the national average. But last year, the 24,000-resident Scott County was the epicenter of one of the biggest American outbreaks of HIV since the height of the AIDS panic in the late 1980s and early ’90s. Over the course of a few months, almost 200 people—nearly 1 percent of the county population—contracted HIV, mostly as a result of injecting prescription opioids with dirty needles. Scott County defied the odds, in the worst way.

Soon, there may be more areas like this. Scott County is but one of many fronts in a public-health war against the threats that have emerged in the weakest parts of the American health-care system. The accelerating opioid epidemic, the threat of Zika, the resurgence of other infectious diseases like West Nile, and ongoing public struggles with obesity and mental health are all foreboding. Partisan differences on public-health policy will dictate how the country faces these mounting health challenges.

As improbable as the Scott County outbreak may have been, health policy in Indiana helped enable it, and eventually stopped it. Mike Pence, Indiana’s governor and the Republican vice-presidential nominee, took stances against clean-needle programs and in favor of criminalizing drug use. These positions have been cited as contributing factors in the creation of an HIV “hot zone” of high incidence and prevalence as the opioid-riddled county and the tiny town of Austin have seen spikes in risky intravenous drug use. Pence eventually went against his deep convictions and allowed clean-needle distribution programs to operate, a decision which seems to have ended the outbreak despite the persistent lack of funding for those programs.

Pence’s initial positions are typical of most Republican lawmakers and of some centrist-leaning Democrats. The outbreak in Scott County could happen in any one of the 17 states—mostly with Republican governors or Republican-controlled legislatures—that don’t have syringe-exchange programs. If anything, Pence’s capitulation on clean-syringe programs and his eventual tepid embrace of Obamacare indicate a sense of pragmatism that goes beyond party dogma.

Most of his positions, however, are firmly within the conservative tradition of health policy, favoring a hands-off policy of few government-sponsored interventions and leaving individuals to their own health-care choices. For many Republicans like Pence, the few exceptions to this rule are for programs for children, retirees, and people who can’t work, and in strictly preventing individuals from making choices, like using drugs, that they see as prohibited on moral grounds. Pence’s decision to defund Indiana’s smoking-prevention programs and slash state public-health budgets are representative of this tradition. His initial stance against syringe exchanges was based in both the market and morality: These programs involve state-sponsored intervention and treat drug abuse as a public-health issue instead of a moral one.

Pence’s conservative vision of health policy contrasts with that of his counterpart, the Democratic vice-presidential nominee Senator Tim Kaine. As governor of Virginia, Kaine presided over an aggressive and controversial public-health policy agenda. One year after Seung-Hui Cho killed 32 people at Virginia Tech, Kaine unveiled an aggressive mental-health-policy plan that provided millions of dollars in funding for expanded services and monitoring for people with mental illnesses. In his first year in office, Kaine was also an ardent supporter of vaccinating girls against HPV with the prescription drug Gardasil. His most significant public-health achievement as governor—in a capital just miles away from the Philip Morris headquarters and in the middle of Big Tobacco heartland—was a 2009 ban on smoking in most bars and restaurants in Virginia. That measure had bipartisan support, but the Republican opposition was characterized by classic conservative anti-intervention public-health rhetoric. “I believe very strongly in the power of the free market to resolve the collective wishes of our society,” said the Republican state delegate C. Todd Gilbert in opposition to the ban.

The broad direction of Republican policy: Invest in health only when crises cannot be ignored.

Pence and Kaine are fairly representative of their parties’ postures toward public health. While Donald Trump’s positions on health care seem to change repeatedly, Pence’s ideology is standardly conservative, favoring restrictions on the use of government funds for encouraging behavioral change or providing health-care services outside of public spaces. His preferred policy tool is the free market, and he has written strong positions against “government big enough to protect us from ourselves” in opposition to smoking regulations. His vision is to allow nonprofit groups and businesses to carry out public-health functions. This ideology tends to favor wealthier people and those with better access to market-oriented health services, helping them live comparatively longer and healthier lives. It is a cheap system to implement, and is in keeping with Republican budget-hawk rhetoric.

But there are hidden costs in this kind of system, brought by the health emergencies that tend to result. Outbreaks like the one in Scott County occur in the absence of swift and decisive—and often expensive—interventions, often forcing conservative politicians like Pence to act. His stance on clean-syringe programs and his choice to limit smoking-prevention programs and public-health budgets are easy short-term fiscal decisions, but favor catastrophe even in the face of mountains of scientific evidence: The World Health Organization has repeatedly demonstrated that clean-syringe programs are one of the most effective ways to reduce HIV infections caused by needles, for example. This posture among some conservatives is not so much anti-science as opposed to the primacy of science in decision-making. Free-market and moral ideals are arguably on equal footing with or above scientific evidence.

These priorities tend to lead to individual and system-wide health emergencies. Failures to intervene in intravenous substance abuse and addiction lead to increased emergency-room usage from overdoses and infections. Failures to intervene in smoking lead to hospitalizations and death. It is no accident that one of the major Republican health policies of the past 30 years was the Emergency Medical Treatment and Labor Act, or EMTALA, passed by President Ronald Reagan and a Republican-controlled Congress in 1986. That act guarantees universal stabilization and life-saving treatment for any patient who arrives in an emergency room, regardless of insurance status or cost. EMTALA has been a life-saving law for many citizens, but without a commensurate investment in behavioral interventions, it increased emergency-room usage while offering no plan to address that increase. The end result was a system of runaway expenses that led almost directly to the necessity of modern-day health reform. EMTALA represents the broad direction of Republican policy: Invest in health only when crises cannot be ignored.

Tim Kaine, on the other hand, represents the view among many Democrats that costly interventions and prevention are necessary to avoid costly emergencies, and that provision of public welfare is a good justification for these costs and associated taxes. Anti-smoking and anti-obesity policies have become party standards, as has the decision to treat opioids abuse as a public-health issue. Hillary Clinton’s proposed health-care reforms, along with President Obama’s 2010 legislation, are billed as an approximation of that ideal: They try to couple nearly universal health-care access with a national platform for public-health interventions. Obamacare’s liberal system of reducing individual costs, providing subsidized health services, paying for prevention, and imposing interventions certainly aims to reduce the chances of dire health emergencies and their catastrophic costs down the road, but is also expensive in the near-term. In fact, it is simply unclear how affordable Obamacare’s provisions will eventually be, for either private citizens or the federal government.

While it’s tempting to see the Affordable Care Act as a decisive victory for the progressive view of public health, emergent health problems shows that America is still caught between two visions of public health. Congress’s failure to fund Zika prevention is indicative of a system that still favors fighting identifiable and clearly dangerous emergencies after they take hold. The opioid epidemic is at least partially the result of system in which government public-health services, hospitals, insurers, and doctors cannot coordinate with each other, along with laws that criminalize drug use, creating the perverse incentive of jail for disclosure instead of treatment. The long-standing decision by Congress to refuse to provide federal funds to study gun violence as a public-health problem—even as it looks more and more like an epidemic—might end up with the same result. The American health-care system is still best suited to fight crises instead of prevent them.

Trump or no Trump, it is a safe bet that any Republican presidential ticket in 2016 would favor the kind of detached, solely market-based system that led to an HIV outbreak in a county of 24,000 people in Indiana. The allure of such a system is undeniable: It would be initially cheap and may even create jobs or short-term economic growth. But as public-health problems like the opioid crisis exacerbate American health-care weaknesses; as emerging diseases like Zika flourish in a hotter world; and as diseases of inequality like HIV resurface in an increasingly unequal country, the health costs will eventually come, and Americans will carry them. Most will pay with taxes. But many will pay with their lives.