Sometime during the next President’s term, her or his national security team may be summoned to the Oval Office to discuss a catastrophe of historic proportions: more than one million deaths in just a few weeks in a far corner of the world, sparking the fall of several governments, giving rise to a violent regional conflict over scarce resources, and unleashing a refugee crisis as fleeing victims encounter panic and closed borders at every turn. Worse still, the President will be told, there is an increasing risk that such death and disruption may soon arrive in the United States.

The cause of such a crisis could be a series of terrorist dirty bombs, or a weather disaster (or famine) exacerbated by climate change, or a rogue state with biochemical or nuclear weapons. All of these are possible. But the single most likely cause of such a nightmare scenario is not any of these oft-discussed security threats but an oft-overlooked one: pandemic illness.

The mosquito-borne Zika virus has been in the news lately, but the threat it poses pales in comparison to a highly infectious, deadly disease that could kill millions, topple governments, and spread with stunning rapidity in today’s interconnected world. No wonder Bill Gates has said that a pandemic “is the most likely thing, by far, to kill over 10 million excess people in a year”—and why he recently forecast a “better than 50/50 chance” that we will see a global pandemic that kills more than 30 million people in his lifetime.

So as the next President maps out plans to combat war and climate change, terrorism and ethnic conflict, humanitarian challenges and sectarian strife, he or she should also make a high priority of the national security threat that has killed more humans than all wars, terrorist attacks, and natural disasters combined: infectious diseases.

This frightening scenario might seem like something out of a science fiction movie had it not been for a recent event that gave us a taste of the devastation an infectious disease can cause: the West African Ebola epidemic. While public health experts and historians will spend decades dissecting exactly how it happened, three lessons are already clear enough that the next President should internalize them before taking the oath of office.

First, it did not have to be this bad. Ebola outbreaks are inevitable; the outbreak that started in Guinea in 2013 was actually the twenty-third known outbreak of the disease. So why did the world’s twenty-third Ebola outbreak become its first Ebola epidemic? While there were a number of reasons, a critical factor was a failure of health authorities, especially the World Health Organization (WHO), to sound the appropriate alarms early enough, and to maintain initial efforts to combat the disease when it (falsely) appeared to be diminishing in the spring of 2014. If the right steps had been taken at the right time, the ghastly tragedy that unfolded in West Africa over the past two years could have been substantially prevented.

Second, it could have been much, much worse. If the Ebola epidemic was not inevitable, its subsequent reversal was likewise no sure thing. In September 2014, a leading forecast projected more than one million Ebola-related deaths in West Africa from the epidemic. This prediction actually understated the risk because it did not include deaths that would have resulted if the disease had spread widely in Africa (as was likely if infection rates had continued to rise in the three heavily affected West African countries). In the end, the death toll was limited to just 2 percent of the horrible forecast.

How were so many lives saved? The bulk of the credit should be given to the people of the affected countries themselves, for making hard cultural and behavioral changes to slow the spread of the disease and taking courageous steps to care for their family members and neighbors. But this locally powered effort was substantially aided by an unprecedented global response—a response led by the United States, which sent over 10,000 civilian government workers, volunteers, and contractors, and over 3,000 U.S. troops. Thousands more Americans went to West Africa as volunteers through NGOs, religious groups, and medical associations.

President Obama deserves particular credit for mustering a whole-of-government response that dispatched critical assistance to West Africa, quickly ramped up Ebola treatment centers in the United States, vastly expanded testing capacities, imposed screening systems at airports, accelerated new vaccines and therapeutics, and deployed an evacuation plan to save international health-care workers. The President opposed a ban on travel from the region, and demanded that science—not fear—govern quarantine policies. A bipartisan majority in Congress funded over $5 billion for the response, without including travel ban legislation. All in all, at a time of great cynicism about our government, the Ebola response was an impressive demonstration of how government can keep us safe, respect civil liberties, and save lives.

Third, we still have a long way to go to be ready for the truly dangerous global pandemic to come. In some ways, Ebola was an “easy” test of the global response systems for a pandemic: It is a hard disease to transmit, it erupted in three countries with relatively small populations and that do not send huge numbers of travelers out of the region, and the affected nations—Liberia, Guinea, and Sierra Leone—all welcomed outside help (including those thousands of uniformed U.S. soldiers).

But the next President could face a more challenging scenario. A future epidemic could be transmitted by airborne means (not just by direct contact with bodily fluids, like Ebola) and therefore be far more contagious. Worse still, the next epidemic could break out in a nation with a global megacity where it would spread rapidly. Imagine a pandemic in Karachi, Mumbai, or Rio, with tens of millions at risk. The next epidemic could occur in a center of commercial power that sends thousands of travelers around the world each day: India, for example, sends more travelers to the United States in a single day than Liberia, Guinea, and Sierra Leone send here in three weeks. And the President could be facing a crisis in a country that would resist the intervention of outsiders (particularly U.S. troops), such as Pakistan. Thus, as challenging as the Ebola response was, the next pandemic could be far harder to contain, combat, and arrest—with devastating consequences for our security and our lives.

What can the next President do to prepare for the coming pandemic? The full list is long, but six measures are of particular urgency.

First, get the right structure in place at the White House. While threats like terrorism, climate change, and weapons of mass destruction are all managed by their own directorates within the National Security Council (NSC), responsibility for coordinating policy and interagency efforts to respond to an epidemic is scattered among a variety of directorates reporting to both the national security adviser and the homeland security adviser. This was one reason why President Obama asked me to join the White House staff as the Ebola response coordinator in October 2014, to manage these disparate functions inside the White House and coordinate the work of more than a dozen federal agencies.

Given the threat that epidemics like Zika pose—let alone a more dangerous pandemic—the next President should put a coordinating unit together before an outbreak begins. A deputy assistant to the President for pandemic prevention and response should be named on the NSC staff, and medical, security, relief, border control, and disaster-response experts on the NSC and Homeland Security Council staffs should be assigned to this new official. The new Pandemic Prevention Directorate should make sure that policy decisions needed to prevent and respond to a pandemic are a priority from Day One in a new Administration, and then should oversee a whole-of-government response if one is needed. We don’t need a Zika Czar, and there should never be an Ebola Czar again either.

Second, create a new Public Health Emergency Management Agency (PhEMA) to mobilize the response to a major outbreak in the United States. At the start of the Ebola response, we had fewer than ten hospital beds nationally that could treat a highly infectious patient with a disease like Ebola; months later, after substantial work and expense, that number topped 100. But in any one city, we never had more than six to eight beds. What if there was even a modest outbreak of a highly infectious, dangerous disease in a city—say, 20 cases at one time—that required the immediate construction of a temporary treatment facility? What if a specially trained workforce of doctors, nurses, and support personnel to treat such patients needed to be isolated, transported, equipped, and housed? What if whole neighborhoods had to be quarantined, or if supplies needed to be delivered to large numbers of potentially sick people? Who would do all this?

The Centers for Disease Control and Prevention (CDC) has trained medical experts, but no real expertise in the kind of logistical challenges and the massive movement of people and equipment that such a task would entail. The Federal Emergency Management Agency (FEMA) would normally handle this sort of work after a natural disaster—but its personnel lack the medical expertise to understand how to operate safely in an environment where an infectious disease is rampant and to resolve the hundreds of medical questions that would be posed by an ongoing response. What is needed, then, is a new specialized agency—a Public Health Emergency Management Agency, or PhEMA—that could combine key resources and talents from these two agencies to prepare for, train for, and then execute a response to a full-fledged outbreak of a deadly infectious disease in an American city.

Third, build on the domestic preparedness investments made during the Ebola epidemic. Remember the anthrax scare in 2001? Immediately after it, the U.S. government spent billions to prepare hospitals to create specialized treatment units, to train response personnel, and to stockpile a variety of equipment. So where was all of that when the Ebola epidemic hit? In the decade after anthrax, as the concern ebbed, equipment was cannibalized for other uses, trained personnel moved on to new jobs in other places, and special treatment units were disbanded.

During the Ebola crisis, Congress appropriated $2 billion for domestic preparedness—to equip infectious disease treatment centers and triage facilities, to train doctors and nurses, and to increase testing capacities. The next President needs to make sure that these investments are not frittered away, as the post-anthrax investments were a decade ago. The one-time funding Congress provided in 2014 needs to be followed with annual funds to keep specialized units intact and well equipped, to train new personnel and make sure previously trained personnel conduct regular drills, and to update lab equipment and protective gear. This way, we can avoid a “restart lag” of preparedness when the next epidemic comes.

Fourth, finish the job on WHO reform and build a multilateral response force. As noted above, the Ebola outbreak became an epidemic largely due to the failure of global health institutions. Chief among them is the WHO, which sounded the alarm about the outbreak too late, failed to develop a coherent plan to respond to it, and never could mobilize key actors to make the response work. Outrage over these failures led many to demand reform of the WHO, but as doubts about the WHO’s response to Zika suggest, the organization is far from fixed, and as Ebola fades from the news, the pressure on the entrenched WHO bureaucracy to reform will fade. The next President cannot let that happen: He or she must make WHO reform a priority of the Administration at the UN, at international gatherings, and at all WHO executive committee meetings.

And because the WHO will never have an effective quasi-military capacity to deploy where epidemic outbreaks happen, the next President must work with our EU allies to create a global “white helmet” battalion that can go into places where U.S. troops cannot to contain a disease and stabilize an affected area. This is an idea being advanced by German Foreign Minister Frank-Walter Steinmeier, and it deserves strong U.S. support.

Fifth, we need a global system to quickly determine which new vaccines and treatments are safe to use, and to compensate any patients injured by these medicines. America is fortunate to have the world’s foremost infectious disease research institution: the National Institute of Allergy and Infectious Diseases, led by the incomparable Anthony Fauci. But its work matters little if we lack a global process to get new vaccines and treatments quickly tested, approved, and administered. During the H1N1 flu epidemic in 2009, thousands of doses of vaccine sat in warehouses because of a lack of an internationally accepted process to approve and administer it, and to compensate individuals who might be harmed by it.

Similar problems required a series of ad hoc solutions during the Ebola epidemic. Promising vaccines and therapeutics had to be administered as part of clinical trials, as we lacked a pathway to authorize and pay for widespread administration of these medicines, and there were heated global disputes over whether anyone injured by these medicines could get compensation. While Gavi, a global public-private vaccine alliance, facilitates millions of vaccinations each year without these structures, its work applies mainly to well-established vaccines—very different from the sort of unproven, quickly developed vaccines and treatments that will be needed in the event of a new epidemic like Zika, and others on the horizon. Now is the time for the world to come together and figure out how to approve new vaccines and treatments quickly, how to set appropriate risk parameters, how to pay for such efforts, and how to compensate any persons injured.

Sixth, and perhaps most importantly, the next President must fund a continuation of President Obama’s Global Health Security Agenda. President Obama launched a Global Health Security Agenda (GHSA) in 2011 to help countries located primarily in Africa and Asia build up their own epidemic detection, treatment, and response capacities. The 2014 Ebola Supplemental Appropriations bill included a substantial boost to the GHSA, but we still have a long way to go. The next President must continue the work to create an “African CDC,” so the nations of that continent are not dependent on our CDC to identify and track infectious disease outbreaks. Ultimately, the only way to prevent a horrific epidemic on our shores is to build national public health capacities in other countries where the threat is likely to emerge. Expanding the GHSA to additional countries, and speeding up its timetable for action in the most vulnerable countries, must be a critical action item for the next President.

The world got a wake-up call in 2014 when it stared Ebola in the face—an epidemic much worse than it needed to be, but ultimately not nearly as bad as it might have been. A far more threatening test of global health systems and international response capabilities is on the horizon, with potentially devastating consequences.

The next President must act from Day One to prepare for that threat: If she or he waits until grim-faced aides file into the Oval Office to explain that a pandemic is unfolding, it will be far too late to save countless people around the world, protect our interests abroad, and preserve lives here at home.