Protesters flooded Manhattan’s public spaces the last two nights, shouting and brandishing signs that read like a disenfranchisement mixtape, from “black lives matter” to “not my president” to “I’m just sad.”

The crowd ranged from abject to furious. But the very act of protesting meant they weren’t hopeless. The worst thing that can happen to a human body, individually or collectively, is a failure of hope.

President Obama reminded us as much on Wednesday, speaking from the White House lawn. “I think of this as a relay race,” he said in his staid way, even as he prepares to pass the baton to a man who spent years claiming that our first black president was lying about being born in the United States. A man who spent much of his own campaign inciting people to despise the most significant legislation achieved by this president—the Affordable Care Act (Obamacare)—as “totally awful” and “the absolute worst.”

There are many ways to hate the current American health-care system, and much reason to. Bernie Sanders amassed ardent support around the idea that medicine is broken because of for-profit insurance companies. They have formed oligopolies that scrape enormous profits out of our suffering, and they are incentivized to provide as little care as possible. To many, Obamacare has taken only complex half-measures to reign this in.

But Trump’s hatred has been contradictory and unclear. Trump has offered almost no alternative and demonstrated much misunderstanding of basic tenets of the Affordable Care Act and the American medical system.

His challenge is to direct this hate productively. Trump does not yet know enough about the system to know what the real problems are. Yesterday Obama implored Americans to “stay encouraged”—not to become cynical. There is hope in the idea that once Trump understands the stakes, his interest in success and winning will prevail.

To say that he will “repeal Obamacare” is much like saying he’ll demolish the subway. Many New Yorkers do hate the subway. It’s often unreliable, it smells, and sometimes rats make it into the cars. It could be a catchy rally cry: Demolish the subway! Indeed, maybe some day a solution will involve tearing up all the tracks and creating an entirely new system of tunnels with really terrific trains. But to start by simply demolishing what we have would destroy the city.

Yet even before Trump takes the oath of office, expect that congress will begin legislation to undo foundational elements of the Affordable Care Act, according to John McDonough, professor of the practice of public health at Harvard. “This would be a momentous move backward, and the nation will be watching.”

It is not a partisan statement to say that this is a move backward: With a full repeal of the law, almost overnight  some 19 million people would lose insurance. That’s according to projections by the Congressional Budget Office. And that number would increase to about 24 million in all subsequent years between 2017 and 2025 (compared with the number projected to be uninsured under Obamacare). Many uninsured would be middle-class people with significant health needs. The United States would have more people without health insurance than any other developed country.

House speaker Paul Ryan said yesterday that Congress would be able to do that easily. Sixty Senate votes would be needed to overcome a filibuster, but the Senate could also use budget reconciliation to avoid filibuster for elements that have significant budget impact—like the expansions of Medicaid and private health insurance that account for millions of newly insured Americans, as well as tax increases on wealthy households that went to fund Medicare.

Republicans got such a bill through Congress in January of this year. President Obama vetoed it. Trump would not.

And that would likely trigger a new death spiral: We’d be back to where we were in 2009. Relatively healthy people could buy a lousy plan for an affordable price. Sick people would be excluded. People in between would pay a lot. When people are uninsured, they’d go to the emergency room for care. The hospitals shift costs to people who are insured. Insurance companies shift costs to employers. Employers shift costs to employees.

Health care is a three-trillion dollar industry that affects every part of our economy. Tracking the downstream effects of millions of uninsured people ties your brain in a knot. And then you, too, have to go to the emergency room.

This is all only to mention the medical-care system, of course. The social determinants of health—the circumstances that shape our daily lives and are the primary factors in our health, like the food we eat, the lead in our water, financial stressors, the safety we feel in our homes and communities, the visceral effects of sexism, racism, and xenophobia—these would remain and demand to be addressed. If Trump follows through with the massive tax cuts he has promised, preventive-health measures and infrastructure would narrow. This will mean only more spending in the medical system to treat problems instead of creating an environment that prevents them.

“I don't think they really want to repeal the whole thing, despite all the rhetoric,” Michael Sparer, chair of the department of health policy and management at Columbia, told me. “You've got 20 million people who have health insurance right now who didn't have it before. Taking it away from them overnight isn't something anybody is going to want to do, politically.”

There are also three million young adults who are getting care through their parents’ insurance, and millions of Americans who are benefiting from other aspects of the Affordable Care Act, like minimum benefit packages and community health centers, a long-standing bipartisan idea.

“It’s one thing to say you’re not going to help people buy health insurance,” said Sparer. “It’s another to say you’re going to take it away.”

Some of the Senators who voted for that Obamacare-repeal measure in January could have been doing it knowing that Obama would veto it, McDonough notes. These Republicans wouldn’t have to return to their electorate and explain why many people are now uninsured. Some may vote differently if and when they understand the consequences.

And there is one other player in this process—the major player, actually—the insurance industry. Pence said during a surreal health-oriented rally last week that he would protect people with pre-existing conditions. This would be the most government-heavy suggestion yet: a law that requires insurers not to discriminate, but without a law that requires everyone to purchase insurance (the individual mandate). The idea speaks to the lack of understanding on the part of the incumbent President and Vice President. The insurance industry is too large and powerful to allow this to happen.

“There are scary things that could happen,” said Sparer. “The worst case scenario for the insurance industry is the conditions that were put in place—that you can't discriminate against people with preexisting conditions, you can't have lifetime annual limits—the nightmare for the industry is that those stay but the mandate goes. That would be fiercely opposed by the insurance industry.”

It was only because those two elements were paired together that the industry allowed Obamacare to pass in the first place—and even still was not happy with it. If Trump decides to take on the industry, he will be taking up Sanders’ cause. This will lead him back toward a single-payer, Medicare-for-all model, where health is in the hands of the people and its elected representatives.

Trump has praised this approach in the past. This is the way that he could be the first president to see an America where every citizen has health insurance. This is the way he could fundamentally disrupt the status quo.

As with New York’s subway system, no reasonable representative would tear up everything without a plan for something reasonable to replace it. Trump will be forced to weigh his promises to “repeal Obamacare” with his desire to be a really great president whose supporters don’t immediately start to hate him when they lose access to health care.

“My guess is there's going to be a lot of talk about repeal, and then the Democrats will filibuster, then Trump will say he's a deal maker and is going to have to negotiate with these terrible Democrats,” said Sparer, “and they will find a way to take out some parts of the ACA while keeping what's working. At which point there's going to be a very difficult and controversial battle about what stays and what goes. The battle over what ‘Trumpcare’ will be is going to be fierce.”

Only after Obama hands the baton to Trump will we know which direction he intends to run. Taking office often has a moderating effect. Even in the spirit of avoiding cynicism, my advice is that if you need any medical care, schedule appointments now. But there is reason to hold onto hope.