Donald Trump made the demonization of undocumented immigrants a hallmark of his presidential campaign. In 2017, Trump, and the administration he heads, continued to target them. In the earliest days of his presidency, Trump falsely scapegoated them as the source of America’s problems. Deportations from the interior of the country soared. And Immigration and Customs Enforcement (ICE) agents started pursuing undocumented individuals in locations like courthouses and hospitals that had previously been safe.

As a medical resident, I regularly see the impact that Trump’s policies and rhetoric have had on this vulnerable population. From the man with congestive heart failure who told me that he would never attend a follow-up appointment with a doctor he did not already know and trust to the woman with uncontrolled diabetes who never filled her prescriptions because she wanted to minimize the time she spent out in public, fears of discovery by federal authorities are shaping how these individuals are interacting with the American healthcare system. And it isn’t for the better.

History has shown that strictly enforcing immigration laws leads to adverse health outcomes in these targeted communities. But the scale of the Trump administration’s operations—and its rhetoric—is unprecedented in modern American history. By inciting nativist anger and pursuing hard-right immigration policies, President Trump is setting the stage for a public health catastrophe.

Anti-immigrant sentiments, and the aggressive enforcement actions that often accompany them, have a chilling effect on vulnerable undocumented populations. In the aftermath of raids by ICE agents, for example, undocumented individuals experience higher levels of fear as the threat of deportation hits home. They also report poorer health and greater levels of psychological distress. Anxiety and depression become all too common.

These feelings are not without reason. In addition to having their lives uprooted, detained individuals are often housed in squalid conditions. Detainees have been denied access to medical care, even in emergency situations, and reports of abuse are not uncommon. Death is the ultimate outcome for far too many people.

To minimize the risk of discovery, many undocumented immigrants have historically found it easier to withdraw from their communities. In addition to disrupting routines, this makes them less likely to utilize public services. After ICE raids, undocumented immigrants are less likely to enroll their children in state Medicaid programs and report crimes to the police.

Like many of my patients, they also forego or delay necessary medical care. After California passed Proposition 187, which set up a citizen verification system and banned undocumented immigrants from utilizing state-run public services, 39 percent of undocumented adults in the state reported that their immigration status made them fearful of receiving medical care. In time, the number of outpatient mental health visits by young Hispanics dropped by 26 percent, and the use of emergency crisis services soared.

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The effects of stricter immigration enforcement efforts are not limited to changes in mental health or how undocumented immigrants engage with society. Recent evidence has shown that they may damage physical health, too. On May 12, 2008, ICE agents raided a slaughterhouse in Postville, Iowa, arresting 389 undocumented immigrants. At the time, it was the largest workplace raid in American history. In the year after the raid, infants born to Latina mothers had a 24 percent higher risk of being born with a low birth weight than infants born the year before the raid. Since the neurocognitive consequences of being born with a low birth weight persist for years, ICE agents may have forever altered the life trajectories of an untold number of unborn babies with a single raid.

As my experiences have shown, worries about the impact of tighter immigration enforcement are not simply theoretical. Not even a year into Mr. Trump’s first term, we are increasingly seeing the havoc his policies are wreaking on the lives of undocumented immigrants. They are showing signs of profound emotional distress. Fears of deportation are paralyzing their communities. And they are increasingly avoiding routine medical care.

Over time, these trends will undermine public health. As undocumented immigrants suffer from increased stress and disengage from society, managing their health will become more difficult. I am already seeing many with chronic conditions present later in the course of their illnesses, which taxes emergency and financial resources. And future infectious disease outbreaks may prove more difficult to control. Without the voluntary participation of all affected patients, documented and undocumented, public health authorities will struggle to track the transmission of any emerging diseases.

Despite these consequences, we are likely to see much of the same from the Trump administration in 2018. Mr. Trump appears to be firmly committed to the hard-line immigration policies that have electrified his far-right base, and he has shown little empathy for the individuals whose lives he has so profoundly affected. There is no reason to expect either of these things to change anytime soon. Long after President Trump exits from the political scene, undocumented communities in America will be suffering from his administration’s actions. The effects on physical health, while still unclear, may begin to appear over the next year.

For those who are be detained, the stakes will be far higher. Conditions in detention centers appear to be worsening under Mr. Trump’s watch—overcrowding is rampant and access to necessary medical care is being withheld, creating fertile ground for a crisis. Sure enough, more people are dying in government custody. This is clear violation of human rights, and there is no justification for it to happen in America. We can—and must—do better.

America was once the place where immigrants came to improve their lives, but that calculation changed in 2017. It will be years before America regains its reputation as “a shining city on a hill”—all thanks to Donald J. Trump.

Kunal Sindhu is a resident physician in New York City. You can follow him on Twitter @sindhu_kunal.