The Trump administration’s latest effort to repel asylum-seekers is getting its day in court, with a Friday hearing in a lawsuit filed by the ACLU and other advocacy groups. But unlike most of the administration’s high-profile legal battles on immigration, which are over policies that have just been implemented or aren’t yet in place, this court challenge targets something that’s been in place for weeks — and quietly expanded along the US/Mexico border.

Since late January, the Trump administration has turned back some Central American asylum seekers to wait in Mexico while their cases are processed. It’s an unprecedented response to what the Trump administration sees as its biggest problem: the fact that growing numbers of people are coming to the US without papers who can’t be summarily detained and deported.

By returning them to wait in Mexico, the administration is allowing them to pursue court cases in the US without actually admitting them.

Initially, the new policy ramped up slowly at a single border crossing. Over the last two weeks, though, returns have started at the port of Calexico in California and at the port of El Paso; additionally, some migrants who entered the US illegally and were then apprehended by Border Patrol agents while on US soil have also been returned.

It’s a fundamental shift in the policy of asylum — which is generally, in US law, a legal protection you claim while on American soil. Instead, many migrants will have to wait in underfunded shelters in Tijuana or overcrowded ones in Ciudad Juarez — cities that aren’t necessarily safe for anyone right now, and where Central American migrants can be particularly vulnerable. (Trump administration officials have responded to this concern by protesting that US cities like Chicago are dangerous too.) US lawyers fear this will make already difficult asylum cases even harder because they can’t provide competent counsel to people in a different country; validating this fear, immigration-court hearings in returnees’ cases so far have been a mess.

Very few Trump administration immigration policies have been in effect for this long without inspiring widespread outrage or getting put on hold by the courts. But the quiet rollout of the “Migrant Protection Protocols,” as the Trump administration calls the program, and the many unanswered questions about the process have made it harder for advocates to attract the attention of American liberals.

In court, meanwhile — despite the many questions the new policy raises about both US and international law — it has taken until now to get a hearing on whether to put the program on hold. It is possible this is a legal battle the Trump administration could eventually win.

1) What is the US’s new policy of returning asylum seekers to Mexico?

Migrants traveling from Central America through Mexico have a legal right to seek asylum in the US. And that right is triggered when they set foot on US soil — which is traditionally where they stay until their cases are resolved.

Under the new policy, though, when migrants present themselves to Customs and Border Protection agents to seek asylum, they’re given a date in a US immigration court 45 days in the future to start their asylum case, and then turned over to Mexican authorities to stay in Mexico until the 45 days are up.

The policy, which the Trump administration calls the “Migrant Protection Protocols” and others call the “Remain in Mexico” policy, applies only to Guatemala, Honduras, and El Salvador (the countries dominating the current flow of families and asylum seekers), and isn’t being used for children trying to enter the US without an adult.

It relies on a rarely used provision in immigration law, which allows the US to return certain people who enter from a “contiguous territory” to be returned to that contiguous territory until their claim for legal status is either accepted or denied. (Whether asylum seekers are covered by the “contiguous territory” provision is at the heart of the lawsuit against the policy.)

Officially, the return-to-Mexico policy is a unilateral decision being made by the US; in practice, of course, it’s happening with the cooperation of the Mexican government.

For the first month, the policy wasn’t in effect along most of the US-Mexico border. But in March, it expanded — first to people who crossed between ports of entry (committing the misdemeanor of illegal entry) and were caught by Border Patrol in the San Diego sector, then to Calexico, and then to El Paso.

Not all Central Americans who enter at those places are being returned. As of March 12, 240 asylum-seekers had been returned over the first six weeks of the policy. It’s not totally clear how officials are selecting which migrants to return — or whether those numbers reflect a slow launch, or resistance on the part of the Mexican government to taking more than a few people a day.

2) Why is the Trump administration returning some asylum seekers to Mexico?

The Trump administration sees pretty much any level of unauthorized migration into the US as unacceptable. And in recent years, an ever-growing share of people coming to the US without papers have been people the US can’t simply detain and deport: unaccompanied children, families, and asylum seekers.

Many of these people don’t ultimately get approved for asylum. Some of them have their claims denied. Some don’t actually file an asylum application, or some don’t show up to court — although evidence suggests this might often be due to people simply falling through the cracks.

The Trump administration has made a concerted effort to reduce the number of people who are free in the US while their asylum claims are pending, so that it can quickly deport those who ultimately lose their cases. It tried several things over the course of 2018: taking in fewer asylum seekers at ports of entry, barring migrants who enter illegally from even applying for asylum, reducing asylum eligibility for victims of gang and domestic violence, making it much harder for asylum seekers to get released from detention, and separating families to keep parents in custody. It’s currently working to finalize a regulation that would allow for the detention of families during the months or years it took for their cases to be finalized.

Most of these efforts have been held up by judges — or, as in the case of the family detention regulation, are expected to face a stiff court challenge. The exception is the capacity reduction at ports of entry — which is essentially keeping asylum seekers waiting in Mexico. It’s both politically and legally trickier to muster opposition to a policy that is happening on foreign soil.

3) How exactly does this work?

The US can’t deport an asylum seeker without at least a screening interview to determine if they have a “credible fear” of persecution. And because about three-quarters pass their screening interviews, asylum seekers have traditionally been able to stay in the US while they wait for their cases to be resolved in court.

The new policy skips that process entirely. Instead of trying to deport immigrants without hearings, it promises them a hearing down the road — and “returns” them to Mexico to wait for those hearings in the meantime.

After a migrant is given notice to appear in immigration court, and a handout with free or low-cost legal providers licensed to practice in that court, they’re told to show up back at the port in 45 days. Then they’re sent back south into the custody of the Mexican government.

Upon return, migrants are given visas by the Mexican government, generally humanitarian visas that allow them to live and work in Mexico for up to a year. Then they’re quickly shuttled into vans and sent to one of Tijuana’s migrant shelters — which don’t always get much notice before they’re expected to receive a group of returnees.

4) How are people able to get a fair hearing in court in the US when they’ve been waiting in Mexico?

The actual hearings in a migrant’s case — in which he can seek asylum or another form of relief from deportation — are still taking place in immigration courts in the US. (In California, they’re happening at the San Diego immigration court; in Texas, they’ll presumably be taking place at the El Paso court.) Migrants are told to show up to the port on the morning of their hearing, and they’ll be escorted by US officials into the US and to the courthouse, then escorted back when the hearing is over — either with a deportation order or (more likely) another court date to continue the case.

What complicates this is that immigration courts are run by the Department of Justice, not the Department of Homeland Security. When the return-to-Mexico policy was first introduced, DHS officials said that DOJ would create a dedicated docket just for these cases, so that they could be scheduled more quickly; DOJ did not do that.

And the few hearings that have happened so far (for the first few people returned under the policy), in late March, have been a total mess.

For one thing, migrants have had tremendous difficulty finding lawyers to represent them in the US while they’re in Mexico. Even before the policy was in effect, US lawyers expressed concern about trying to represent clients who weren’t on American soil; this is a key reason that the ACLU and other groups are challenging the legality of the policy, arguing it doesn’t provide sufficient access to legal counsel.

One migrant told the immigration judge last week that he tried to call the lawyers on the sheet CBP provided, but none of them were picking up because he was calling from Mexico. In general, judges are willing to give migrants extensions to find a lawyer; given the record immigration-court backlogs (and the fact that returnees are on the same docket as all other non-detained immigrants), that extension could drag a case out a long time.

Then there are the migrants who don’t show up on the morning of their hearing — which might not always be the date they were given when they were first returned to Mexico. The first few cases of returnees were moved up several days, and it wasn’t even clear that migrants knew about the rescheduling; DHS prosecutors didn’t have an answer when one immigration judge asked how they could contact people in Mexico to tell them the new date. Other migrants’ hearings aren’t being rescheduled, but they haven’t shown up anyway, for reasons unknown.

In theory, any migrant who doesn’t show up for their immigration-court hearing faces a deportation order in absentia; prosecutors have pushed for that to happen in these cases. But so far, judges have refused deportation orders for returnees who don’t come back to the US for a hearing, given how chaotic the process has been.

In theory, that might seem like a setback for the Trump administration; these cases will now take months longer than they otherwise would, and they’re not securing deportations. But it’s only a problem if the administration’s goal is to minimize the number of open asylum cases. If the goal is simply to prevent asylum-seekers from living on US soil while their cases are adjudicated, the snafus might be worth it.

The immigration-court chaos may, however, strengthen the lawsuit against the new policy, bolstering its claims that it isn’t providing sufficient process to asylum-seekers.

5) Does this violate the US’s humanitarian obligation toward asylum seekers?

The fundamental principle of international asylum law is that you can’t return a migrant to a country where they’re in danger of being persecuted, known as non-refoulement. That’s why the US has to give court hearings or at least screening interviews to people who enter claiming fear of persecution in their home countries.

The involvement of a third country — Mexico — doesn’t automatically let the US off the hook. (The US has a treaty with Canada in which each country is designated as a “safe third country” for asylum: Migrants who come through Canada will be turned away if they try to seek asylum in the US, and vice versa. Mexico hasn’t been willing to sign a version of this treaty.)

So the US is prohibited from returning migrants to Mexico if Mexico would return them to countries where they’d be persecuted. Mexico is assuring the US it won’t do that to migrants returned under the remain-in-Mexico policy — that’s why it’s giving visas to returnees who don’t already have them.

Mexico has also (in theory) refused to take back any migrants who are at risk of persecution in Mexico. But there are lots of questions about how the US is deciding that someone’s at risk.

Customs and Border Protection agents aren’t asking migrants if they are afraid of being returned to Mexico, like they do with normal asylum claims. Instead, migrants have to volunteer that information while they’re in initial processing — something that it’s not clear they would know how to do.

If a migrant does mention a fear of persecution in Mexico, she’s supposed to be referred to a US Citizenship and Immigration Services asylum officer for an interview, as in a typical asylum claim. But in the typical asylum process, a migrant just has to establish a “credible fear” of persecution if returned to her home country — a deliberately generous standard. Under the new protocol, a migrant has to establish that she is “more likely than not” to be persecuted if she’s sent back to Mexico, a much tougher bar to meet.

During that interview, migrants don’t have access to a lawyer. (DHS says this is because of space constraints.) And in another divergence from standard procedure, the interviewer doesn’t make the final decision. All reports are referred to someone more senior at US Citizenship and Immigration Services for review.

It’s not clear how many migrants are being screened for fear in Mexico, and how many are passing those screenings. To human rights advocates, though, the difference between the new process and the typical way migrants’ fear is assessed is a red flag that some people with legitimate persecution claims might be falling into the gap.

6) Are people safe in Mexico while waiting?

President Trump loves to talk about how dangerous the Mexican side of the US-Mexico border is. But a fundamental principle of the US’s cooperation with Mexico to return Central American asylum seekers is that Mexico is a safe — or at least safe enough — place to wait.

When the US “unilaterally” announced it was starting returns to Mexico, the Mexican government stated it would ensure the safety of Central American migrants while they waited.

Migrants themselves, however, hardly feel safe. Tijuana is still trying to adjust to the large population of waiting asylum seekers (those who haven’t been admitted at the port yet, as well as returnees), while dealing with a drug-trade-induced crime wave.

One returnee, interviewed by Vox in Tijuana last month, said his friend had been harassed and robbed by police; when Vox asked if he felt safe in Tijuana, he answered, flatly, “No,” and started rattling off local homicide statistics. Another pair of asylum seekers still waiting to be allowed to enter the port (who could be returned under the new policy if the US chose), answered the same question by saying they didn’t go anywhere — they only left the migrant shelter to go to the supermarket, or to check each morning to see if their number had come up at the port.

As far as the US is concerned, this is simply not their problem. The Trump administration claims it’s meeting its obligation to migrants with its opt-in interview process, because its only obligation is to protect from persecution, not all types of danger.

But it’s very hard to tell the difference in practice between generic danger and persecution. Advocates and migrants both report that migrants in Tijuana are harassed (by criminals and police) because they are Central American migrants. The Trump administration won’t confirm that this would count as persecution that would allow a migrant to avoid MPP and stay in the US. Given that asylum officers are instructed to take the Mexican government’s written assurances of safety into account when determining if a migrant would be persecuted there, there’s no reason to believe it would be.

7) Why is the Mexican government going along with all this?

Officially, it’s not. The government of President Andrés Manuel López Obrador has insisted at every turn that it’s is a “unilateral” decision from the US, and that its only involvement is in agreeing to take migrants while they wait.

This isn’t really true. The question is how much Mexico is doing to collaborate.

The US was negotiating with López Obrador’s advisers over a return-to-Mexico policy before López Obrador was even inaugurated in December 2018. The morning the US announced it would invoke the “return to territory” provision, Mexico had a statement ready promising to receive returnees and keep them safe.

Maybe Mexico is both collaborating and resisting. In general, the arm of the government announcing cooperation with the US on MPP has been the foreign ministry, led by Marcelo Ebrard, a close adviser to the president. But actual implementation of migration policy falls to the interior ministry, led by Olga Sánchez Cordero, which has been much less enthusiastic about it.

Generally, the assumption among US-Mexico watchers is that the López Obrador government is buying goodwill on migration so that it can get more out of Trump on other issues like trade — ensuring that the US-Mexico-Canada trade agreement is ratified, for example. (In reality, it is not at all clear that Congress is paying attention to Mexico’s cooperation on immigration, or would make its decision about USMCA on that basis.) Ultimately, though, why it’s going along is a matter of speculation; that it is going along is not.

8) Is this legal?

A group of advocates led by the American Civil Liberties Union and the Southern Poverty Law Center has sued in federal court to stop the returns of asylum seekers. The lawsuit argues that the Trump administration violated the Administrative Procedures Act by putting a new policy in place without issuing any regulations governing it. (That claim is strengthened by the fact that the US invented a new screening procedure to determine fear of persecution in Mexico — which advocates also accuse of violating the US’s commitment to non-refoulement under international law.)

Most important, though, is the question of whether US law allows asylum seekers to be returned to Mexico to begin with.

The section of US law that the Trump administration is using to justify the policy hasn’t really been used before on any significant scale. And it’s not clear whether it actually applies to asylum seekers. The statute is split into three parts, and it’s not clear which part encompasses the others.

Some immigration law experts argue that asylum seekers clearly aren’t allowed to be returned to a “contiguous territory.” But others — even those not inclined to be favorable to the administration — acknowledge it could go either way.

It’s more similar to the ambiguity of the travel ban — a policy on which the Supreme Court agreed to defer to the executive — than to some of the administration’s more legally questionable policies, like the thwarted asylum ban.

9) Will this just go the way of Trump’s other fights with the courts?

Even the travel ban initially got held up in court in California. So did the asylum ban, family separation, the family separation policy, efforts to restrict grant funding to so-called “sanctuary” jurisdictions, and the effort to end the Deferred Action for Childhood Arrivals (DACA) program. Trump’s distrust of the “liberal Ninth Circuit” appears to be mutual.

Yet MPP has been in effect for more than a month. It’s expanding. And while it could be put on hold at any time after Friday’s hearing, it might not.

The secrecy and opacity around MPP has made it harder to sue over the program. Advocates didn’t want to file a lawsuit before MPP went into effect, because they didn’t know what they were arguing against until they could see it happening on the ground. Because of that, when the litigators (led by the ACLU and SPLC) asked the courts for an immediate “temporary restraining order” stopping the program, the judge said it wouldn’t be appropriate to restrain a policy already in effect — and made the ACLU and the government agree to a schedule to consider a slightly less immediate “preliminary injunction” instead, which is what Friday’s hearing is about.

But even now, the lack of information about (in particular) the “fear in Mexico” screenings makes it very hard for a judge to rule that MPP meets the standard of apparent illegality needed for a preliminary injunction. Meanwhile, the Trump administration is trying to get the case moved to a different court — one that might rule that immigration advocacy organizations have no right to sue on behalf of asylum seekers who aren’t yet their clients and dismiss the case entirely.

Perhaps most importantly, the involvement of the Mexican government — however coerced it might be — distinguishes this from other Trump immigration policies. Immigration policy always overlaps somewhat with foreign policy; that’s one big reason the courts have traditionally deferred to the executive branch on the issue. But in this case, the foreign policy angle is explicit. It’s central to the policy. And US courts are extremely wary of reviewing foreign policy.

It is of course generally a bad idea to bet that federal judges in California will side with Trump on immigration. But it’s also a bad idea to assume that because judges have generally stopped Trump’s immigration policies, MPP will meet the same fate. It might, quietly, be the Trump administration’s most sweeping success in keeping asylum seekers out of the US.