North America has long been a geographic term, not a political or a cultural designation. But, in the twenty-five years since the institution of the North American Free Trade Agreement, it has come to seem not entirely delusional to think that North America might be a real entity, one whose peaceful northern border simply dissipates into the Arctic, and whose fractious southern border is in the middle of the Lacandon Jungle, which covers Mexico’s border with Guatemala, in what was once the heart of the Mayan civilization.

Sketch a perimeter around the four American and four Mexican states that touch the Rio Grande, as advocates of a North America are fond of doing, and you have the world’s fourth-largest economy. Since 2009, there has been slightly more migration headed south across the Rio Grande than north, the numbers shifting with the relative strength of the job markets on either side of the border. This is the kind of movement you might expect between regions of the same country, not between a poor and dangerous country and its wealthy and safe neighbor.

This North America has a weakness, at least in the United States. It was assembled through economic and bureaucratic coöperation—through NAFTA and the Mérida Initiative, which began in 2008—and not through popular politics. It has been far less visible in our daily politics than the European project has been on the Continent. The project of North America is neither nationalist nor universalist, so it does not fit the current mood on either the right or the left. It came out of the internationalist wing of the Republican Party and the pro-business section of the Democratic Party, both of which have been effectively dust-binned by voters. Now travellers arriving in Mexico have their names checked against security databases, and plainclothes U.S. Customs and Border Protection agents patrol the Mexico City airport. Automobiles leave Mexican plants halfway assembled and go to American plants, where the job will be finished.

The immigration question, as it intensified in the last two years of the Obama Administration, was generally misunderstood. It did not depend upon what was happening at the southern border of the United States but on what was happening at the southern border of North America. The majority of migrants caught at the Mexican border were from other places, mostly the small and increasingly unstable nations just to the south of Mexico. At the Texas border in 2016, four out of five migrants came from Central America, which escalating criminal violence has made more hazardous than many other places on Earth.

Had this happened earlier in the Obama Administration, when Janet Napolitano’s Department of Homeland Security was deporting record numbers of migrants, the American response might have been harsher. But, by 2014, the Administration’s relation to immigration had grown more complicated. Comprehensive immigration reform had failed, after conservative anger at the grassroots level made Republicans reluctant to cut any deal. But the plight of the Dreamers—immigrants who were brought to this country illegally as children—captured national attention. And the initial response to the surge of Central American refugees—housing them in detention facilities that were soon overwhelmed, and often separating families—seemed inhumane.

By January, 2016, some doubt had crept into the Obama Administration’s position on immigration. That month, coördinated nationwide raids by Immigration and Customs Enforcement ended with only seventy-seven deportations. One former Administration official told me that there were suspicions that warnings about the raids had leaked to activists, so many of ICE’s targets had known not to be home. At the border, immigration officials frequently gave preliminary approval to the asylum claims of Central Americans who said they were fleeing violence. “Smugglers were no longer trying to get past the border patrol. They were trying to get caught by the border patrol,” Alan Bersin, who ran C.B.P. for Obama, told me over the weekend.

Last week, just before Secretary of State Rex Tillerson and Secretary of Homeland Security John Kelly set out on a diplomatic trip to Mexico, reporters from ProPublica and Univision broke a strange piece of news: The Department of Homeland Security was planning to deport non-Mexican migrants to Mexico. The policy seemed to be aimed at Central Americans migrants, many of whom remain in the United States while waiting for their asylum claims to be processed. Sending these people back to their home countries could lead to a humanitarian disaster, so the idea was to send them somewhere else. “If you want to make a claim for asylum or whatever, we’ll hear your case, but you are going to wait in Mexico,” a D.H.S. official told ProPublica and Univision. But Mexican law made no provision for migrants like these, and the Trump Administration had not coördinated the plan with the Mexican government. “There are elements,” the D.H.S. official allowed, “that still need to be worked out in detail.”

At a press conference in Mexico City last Thursday, Kelly and Tillerson took pains to explain that some of the President’s most eye-catching statements would not be encoded in policy. Trump had spoken of a “military operation” at the border. Kelly said that there would be “no, repeat, no use of military-force operations. None.” During and after the campaign, Trump had promised “mass deportations.” “Let me be clear, there will be no mass deportations,” Kelly said. But neither he nor Tillerson offered any clarity about whether the United States really planned to send Central American migrants to Mexico. Several days later, it turned out that the Mexicans had rejected the idea. “We told them it is impossible,” Miguel Ángel Osorio Chong, Mexico’s interior secretary, told a radio interviewer this weekend. “We [the U.S. and Mexico] need to assume regional leadership for the development of Central America,” Luis Videgaray, the Mexican foreign minister, said. This just emphasized the gap between the two governments: to the White House, Mexico lay on the other side of a barrier that ought to be stronger; to Mexico, what was at stake was the partnership of a greater North America.

Bersin happened to be in Mexico during Tillerson and Kelly’s trip, and he told me that the general response to their remarks was relief mixed with confusion. The people running ICE and C.B.P. had worked under Obama’s White House. Trump’s far more aggressive posture was another matter. “Like much of the rest of the world, they are mystified about who to trust,” Bersin said, of Mexican officials. He compared Kelly and Tillerson’s Mexican mission to Mike Pence and James Mattis appearing at the Munich Security Conference, where they sought to reassure a jittery Europe that the United States was still on its side. Bersin was optimistic. In the debates within the White House, he said, “my money’s on Kelly and Tillerson.” But that did not diminish their task.

“In the American imagination,” the Princeton sociologist Douglas Massey wrote last year, the border between Mexico and the United States is “a symbolic boundary between the United States and a threatening world. It is not just a border but the border.” Now, establishment figures are trying to convince a populist President that the border matters less than he thought, an idea they could never sufficiently impress upon the American people. In the Clinton years, the hope was that, once NAFTA took effect, its benefits would strengthen its popular constituency. But those benefits were often invisible and uneven, and the constituency for the idea of North America often seemed to be only those who worked to sustain it.

Now NAFTA’s benefits may be taken away, they have become easier to see. In the Central Valley of California, Republican farmers have wondered who will pick their crops. In Texas, the right-wing state agriculture secretary travelled across the border last week to argue that Mexico “must have input” on any border wall. In a pro-Trump Illinois coal town, residents reacted with anger when an immigration dragnet picked up the beloved manager of a local Mexican restaurant, who had a couple of old arrests for drunk driving. The confusion, in these places, stems from the fact that they are not just conservative precincts of the United States; they are also residents of a more notional place, of North America.