The wisdom of each of those measures will be sorely tested now, as the coronavirus threatens to morph into a full-blown pandemic. More than 100,000 people across more than 80 countries have been infected with the new virus — and more than 3,400 of them have died, including at least 14 in the United States.

Proponents of closed borders and small social safety nets have a tendency to highlight the tension between citizen and noncitizen, to imply or explicitly state that the only way to help one group is to deprive the other. But the truth is, people on both sides are hanging by a thread.

Infectious diseases, especially those like Covid-19, have a knack for penetrating and exposing such false dichotomies. Already, citizens who are underinsured or uninsured are being slammed with medical bills that they can’t afford when they seek testing and treatment for the virus. Unsurprisingly, experts say that many of them are bound to avoid such care as the outbreak rages on. If quarantines become routine, tens of millions of low-wage workers, many of whom don’t have health insurance or paid sick leave, will not be able to stock up and stay home. One shudders to think what will happen if the courts dismantle the Affordable Care Act in the next year — a move that could ultimately leave 21 million or so more people without health insurance.

Among noncitizens, the effects of the public charge rule and other fear-based immigration policies have long been apparent. New mothers are turning away free baby formula. Hungry families are turning away food assistance. The chronically and even fatally ill are avoiding hospitals and rejecting medical care. In 2019, The Atlantic reported that at least 200 eligible families in a Virginia county had stopped accepting WIC and that many were also turning down reduced-price lunches. Both of those programs are exempted from the public charge rule — using them will not count against a person’s visa or green card application — but those families were too afraid to chance it.

It’s easy to see how all this fear might feed on itself in the months ahead and also where that might lead. If citizens struggling to cover their own health care nurture resentments against any group perceived to be getting help to which they themselves are not entitled — or worse, if they grow xenophobic and subscribe to the notion that immigrants carry diseases — they might be compelled to endorse policies even more draconian than those already in play. That would create more anxiety among noncitizen communities, which would lead to fewer people seeking medical care when they need it. From there, the epidemic would only get worse.