Starting at midnight tonight, and for the next 90 days, people who cross the US/Mexico border without papers will not be eligible for asylum unless they wait at ports of entry — official border crossings. A presidential order signed by Trump Friday morning made the new policy official.

Under US law, people who enter the US without papers are legally able to apply for asylum unless they are subject to specific restrictions. This policy — enacted via a regulation formally issued Friday morning, and Trump’s presidential proclamation signed soon after — turns that on its head. It adds a restriction that would affect the majority of the 10,000 people a month — most of them Central Americans, and many of them families — currently turning themselves in to border agents in hopes of being protected from violence in their home countries.

It will force asylum seekers to choose between having to wait for weeks or longer at overloaded ports of entry — unless they’re prevented by smugglers from coming to a port at all — and risking near-immediate deportation by crossing illegally and turning themselves in to Border Patrol.

The substance of the administration’s new policy is guaranteed to face a lawsuit — and will probably be put on hold at some point by a federal judge, as past Trump immigration actions have been. So will the methods by which they’re enacting it.

The ban was activated by a proclamation Trump signed under the same provision of the Immigration and Nationality Act that he used to sign the “travel bans” of 2017 (the last of which was upheld by the Supreme Court in a ruling in June 2018, and is still in effect). But the groundwork for it was laid by a regulation that went into effect immediately go into effect immediately when it was formally published in the Federal Register Friday — an unusually aggressive move.

In theory, the ban could be lifted if Mexico agrees to sign a “safe third country agreement” with the United States — which would allow the US to turn back all asylum-seekers who had traveled through Mexico. (The US currently has such an agreement with Canada.) A safe-third-country agreement would essentially make the current Central American migration, which has brought hundreds of thousands of people from Guatemala, Honduras and El Salvador to the US and Mexico to seek asylum in the last several years, Mexico’s problem alone to solve. Mexico, whose new president will arrive in office on December 1, has shown no interest so far in signing such an agreement.

People affected by the new policy will still be able to seek humanitarian protection. However, they will be subject to a much higher screening standard to stay in the US and pursue their cases (as opposed to being immediately deported) than asylum seekers currently are. Instead of being held to a standard that 75 percent of people currently pass, they’ll be held to one about 25 percent of people pass.

And even the people who pass that screening will only be eligible for lesser forms of legal status that don’t offer any opportunity to stay in the US permanently.

The two-part policy change will affect thousands of people currently on their way to the US. A large share of asylum seekers will go from having a very good chance of being able to stay in the US and work legally during the months or years it takes to pursue their asylum claim, to having a very good chance of being summarily deported a few days after their arrival.

What the new asylum policy will change

Here’s how it works until midnight Friday night: Someone who enters the US without papers — either at a port of entry or otherwise — is subject to immediate deportation without a court hearing, unless she says she wants to claim asylum or that she fears persecution in her home country. In those cases, she’s entitled to an interview with an asylum officer.

Generally, if the asylum officer determines that she has a “credible fear” of persecution (in other words, that there’s a significant possibility she’d be persecuted if deported based on her race, nationality, religion, political opinion, or membership in a particular social group), she is allowed to go before an immigration judge in the same court process that unauthorized immigrants arrested while living in the US are entitled to. There, she’s able to make her case for asylum. And in the meantime — since immigration court hearings take months or years — she’s legally able to work and live in the US.

Even if she is being persecuted, she might still be ineligible for asylum — if she has a certain criminal record in the US or her home country, for example. But the judge will wait until the end of the process to make that judgment. If she is ineligible for asylum but still has reason to fear persecution, she can receive a lesser form of protection — called withholding of removal — that allows her to stay in the US but gives her no path to permanent legal status.

Here’s how it will work as of midnight Friday night: Someone who enters the US without papers between ports of entry, from Mexico, will still be entitled to an interview with an asylum officer. But if she entered between ports of entry, the asylum officer is required to say that she does not have a credible fear of removal. Instead, he’s supposed to screen her for a reasonable fear of removal — a standard that requires not just a significant possibility of persecution but a determination that persecution is more likely than not.

The “reasonable fear” standard is used only in rare cases under the status quo — for immigrants who’ve already been ordered deported and returned to the US, and immigrants who have committed serious crimes. But the difference in pass rates is striking. In credible fear interviews, about 75 percent of all asylum seekers pass. In reasonable fear interviews, a little more than 25 percent do. Even assuming that many asylum seekers who are currently subject to the credible fear standard would also pass the more stringent one, that’s still thousands of immigrants a month who would end up failing their screening interviews and being summarily deported.

People who do pass the reasonable fear screening will be allowed to go before an immigration judge. But they still wouldn’t be eligible for asylum. Their only options would be withholding of removal and protection under the Convention Against Torture. That allows the US to fulfill its obligations under international law — which prevents countries from returning migrants to places where their lives are in danger — but doesn’t give people any access to permanent legal status. (This Vox article offers more detail as to how this “withholding-only” process will work.)

The Trump administration is coming closer than ever to using executive policy to override a law written by Congress

The Trump administration has a long track record of having its immigration policies put on hold (or struck down entirely) by federal judges. The first travel ban in January 2017; the family separation policy in June 2018; a host of setbacks on various fronts in its battle against sanctuary cities; its court-thwarted efforts to end the Deferred Action for Childhood Arrivals (DACA) program — at this point, it’s fair to say that litigation is expected whenever the administration makes a move.

But even for the Trump administration, this policy is a bold assertion of executive power to restrict immigration to the United States.

The text of the Immigration and Nationality Act specifies that people may apply for asylum “whether or not” they enter the US at a port of entry. The Trump administration is setting up to render that “or not” basically dead letter — at least as long as the expected proclamation is in effect.

The administration justifies this by saying that the law also gives the attorney general broad power to set restrictions on asylum, and the president broad power to suspend entry (an interpretation encouraged by the Supreme Court’s ruling in the travel ban case in June, which didn’t actually specify any limits on this power).

It’s the typical strategy on immigration under Trump: finding parts of the immigration system where the executive branch is given a lot of discretion, and use that discretion as aggressively as possible.

But this comes darn close to using executive discretion to override a specific thing that Congress wrote into the law.

It is near-certain that the policy will be subject to a lawsuit in the immediate future — maybe even before the policy even goes into effect at midnight Saturday. It is extremely likely that the policy will be put on hold by a federal judge ruling against the administration soon after that.

The Trump administration, according to Julia Ainsley of NBC, thinks it’s going to prevail with the newly ensconced conservative majority on the Supreme Court. It might be right. But it’s going to be a closer call, on the law, than the travel ban was. It’s the riskiest fight, legally speaking, the administration has picked yet.