On Tuesday, the Boston Globe published a letter from Francisco Rodriguez, who had written it from a jail in Suffolk County, Massachusetts, where he has been held for the past week. Rodriguez, who is forty-three, has lived in this country for a decade. For the past five years, he has worked as a custodian at the Massachusetts Institute of Technology, where he belongs to a labor union. He pays taxes and runs a carpet-cleaning business on the side. He is married, with two children, and his wife is pregnant with a third. Prior to his current incarceration, he wrote, he had never been arrested for any crime.

Rodriguez is from El Salvador, where he worked at an engineering firm, but he left the country in 2006, fearing for his life, after gangsters murdered one of his colleagues. He reached Boston without documentation and applied for asylum but was denied. His appeals ended in 2011, and he became subject to deportation. Each year since, however, officials at the Department of Homeland Security have granted him a stay against removal, after he has met with them to insure that he has remained a resident in good standing. This spring, however, following the election of Donald Trump, Immigration and Customs Enforcement agents, who are part of D.H.S., sent a different message: Rodriguez needed to buy himself a ticket to El Salvador and volunteer to surrender for deportation. An invitation that had been a routine check-in in previous years suddenly became an order to leave the country. “I was told that if I did what ICE said, I would not have to be in jail,” Rodriguez wrote in his letter. “I believed them. I came when they told me and did what they said, but they took me. I do not understand why I am here.”

The reason, in fact, is no mystery. The same day that Rodriguez’s letter appeared in the Globe, the latest effort to repeal and replace Obamacare collapsed in the Senate. Trump issued Lear-like tweets, threatening to allow the health-care system to implode in order to create conditions in which a compromise is born of necessity. It was the latest evidence that the Administration, and the divided Republican Party, are failing to govern. A number of the Trump campaign’s promises—health-care reform, infrastructure spending, the wall—appear to be foundering. Immigration is one area where the President can deliver, to a substantial extent, on his incendiary words, without Congress. (Trump wants to increase spending dramatically on immigration police, to accelerate deportations, and Congress will have a say about that, but the President’s authority to reset detention priorities is broad.) And the more Trump fails at other parts of his agenda, and the more he doubles down on a strategy of pleasing his core supporters, the more unconscionable cases, like that of Francisco Rodriguez, there will be.

President Obama deported more people than any of his immediate predecessors did—a record that is a stain on his legacy—but he did change course during his second term, to insure that ICE prioritized the deportations of felons, not of law abiders. “After eight years of struggle, we ended up with a very substantial decline in deportations under the Obama Administration, and the key to that was the establishment of enforcement policies that began—not consistently, but more and more—to filter into the conduct of ICE agents,” Deepak Bhargava, the president of the Center for Community Change, a nonprofit advocacy group that works in low-income areas, told me. “Essentially, what this Administration has done is undo the whole concept of prosecutorial discretion.” This has “empowered the worst rogue ICE agents, who can act as they want.”

Rodriguez’s case has become a cause célèbre at M.I.T. The university arranged for an attorney to represent him pro bono. His union, S.E.I.U. Local 32BJ, has advocated for his release, and a public rally for his freedom attracted about a thousand people from the community. A judge has stayed his removal from Massachusetts, but his ultimate fate is uncertain. For one thing, it’s not clear whether, at today’s ICE, having the support of an institution like M.I.T. is likely to help your case or hurt it. For another, Marielena Hincapié, the executive director of the National Immigration Law Center, told me that the Trump Administration, pandering to nativists demanding that every undocumented resident of the United States be thrown out, has “done away with priorities altogether.” Day to day, from city to city, prosecutorial discretion at ICE “is about the individual agent looking at the totality of circumstances and trying to decide whether to detain or deport” a person—a form of discretion similar to that exercised by police officers in their daily duties. Without clear guidelines, and in an atmosphere of hatred and demagoguery, there is now, Hincapié said, “such a level of chaos and fear.”

How bad could things get? Under Obama, the D.H.S. stepped up deportations as part of a political strategy to persuade Republicans that the Administration was serious about law enforcement, in the hope that this would produce a grand compromise on immigration reform—one that would create a path to citizenship for people like Rodriguez. It didn’t work out that way. At the end of Obama’s first term, the United States was deporting more than four hundred thousand people a year. By the end of his Presidency, the number was less than half that. Now Trump officials talk about deporting as many as eight million people.

Two very large groups of undocumented immigrants are particularly vulnerable. First, there are more than three hundred thousand people, mainly from Central America and Haiti, who legally reside in the United States under “temporary protected status,” which was granted because of Central America’s civil wars and, in the case of Haiti, the devastating earthquake of 2010. These official reprieves expire on a rolling basis, usually every eighteen months, and, although the Trump Administration decided last spring to extend affected Haitians’ protected status for six months, advocates for immigrant rights are skeptical that this policy will continue.

Then there are the “Dreamers,” undocumented American residents who came to the United States as children and who therefore cannot be held accountable for having arrived without papers. According to the Center for Community Change, there are about seven hundred and eighty thousand Dreamers. Obama used his executive power, during his second term, to create a program that allowed these residents to obtain work permits and to enroll in universities. After Trump’s election, there was widespread fear that Dreamers would be arrested, but, this spring, Trump said he would extend the program. He seems to have a soft spot, appropriately, for this segment of the population. After the spring announcement, “everyone breathed a sigh of relief,” Kica Matos, the director of immigrant rights at the Center for Community Change, said.

But that respite has proved short-lived. Attorneys general in Texas and other states who challenged Obama’s policy have threatened the Trump Administration with legal action if by early September it doesn’t rescind the privileges granted to Dreamers. Even if the Administration wants to fight back, the man in charge would be Attorney General Jeff Sessions, an anti-immigrant hard-liner. Still, Hincapié noted, because of the resonant appeal of the Dreamer cause, “if the Trump Administration decides to terminate the program, it really will feel heat from not just the immigrant-rights community but from many, many others.”

Rodriguez is not a Dreamer, but his story is a moving one. The support extended to him is encouraging, wherever it leads. It shows that large numbers of Americans understand the moral and economic imperatives of normalizing the lives of law-abiding undocumented residents, here in a country founded on, and made great by, the aspirations of immigrants—those with papers and those without. Yet the Rodriguez case is also saddening. It unfolded in Cambridge, a hotbed of liberal activism, but it still constitutes a difficult struggle with uncertain results. The case suggests how many hundreds or thousands of other people may now, or may soon, be detained and deported without visibility, without legal advice, without reasonable cause, at the expense of their families—and to the deepening shame of America’s place in the world.