On Friday, the Trump administration announced that it was ending the practice called “catch and release” at the US-Mexico border.

If it were that easy, they wouldn’t even have needed a memo.

While the idea of “catch and release” has been part of the immigration debate on and off for more than a decade — and President Trump has used the phrase repeatedly in recent days — what it means hasn’t stayed consistent. This White House tends to use it as, well, a catchall term for any law or policy that prevents the federal government from keeping every single immigrant apprehended without papers at the US-Mexico border from being processed (and, they’d prefer, deported) as quickly as possible, and being kept in immigration detention in the meantime.

But those policies can’t be changed by executive fiat — in fact, the memo “ending” “catch and release” actually acknowledges that Trump can’t end it on his own.

The memo signed Friday directs the three Cabinet departments that deal with immigrants apprehended entering the US to tell the administration what steps they’ve taken to expand the capacity and use of immigration detention.

But it also directs them to come up with “additional resources or authorities” that they’d need in order to detain even more immigrants — a subtle signal that the administration sees the border as a top legislative issue too.

The Trump administration can only tighten the screws on immigrants; it can’t slam the door on them entirely. The laws and policies that Trump and his officials refer to as “catch and release” are actually legal protections for specific vulnerable populations — groups like children, families, and people who claim they’re in deadly peril if they’re sent home — that Congress and the courts have decided need to be treated with extra care.

The White House disagrees. To the administration, anyone crossing into the US without papers should be treated as a potential invader, and anyone who disagrees doesn’t believe in borders. But it is rapidly approaching the limits of what it can do on its own to put that vision into practice.

The push to end “catch and release” is designed to push the federal government as far as it can legally go right now to make detention and deportation the rule for everyone crossing into the US without papers — regardless of circumstance — and to put pressure on Congress to change the laws to let the government go further still.

“Catch and release,” explained

You can’t understand why “catch and release” is suddenly the Trump administration’s biggest target without listening to Trump himself. But you can’t really understand what “catch and release” is by listening to Trump, either.

Here’s how Trump explained it to a crowd at a West Virginia event (ostensibly about tax reform) on Thursday:

we have a country where if they step one foot — not two feet — if one foot hits our country, we have to take those people gently, register them, and then release them. Okay? We’re going to release them, essentially, in a short period of time. So we release them. And then they’re supposed to come for a court case. [...] We release them. They go someplace into our country. They’re supposed to come back within two or three years for a court case, but nobody ever comes back.

Trump’s basic premise is mostly wrong. As a rule, the US government detains and deports anyone it catches crossing the US-Mexico border. The screws the Trump administration is now trying to tighten are the exceptions to the rule: extra legal protections in place for people who claim they’re in deadly peril if they’re sent home, or who come as families or as children on their own.

Rhetorically, the trope of widespread, pernicious “catch and release” should be understood as a new variation on Trump’s favorite themes: that immigrants are infiltrating the homeland and importing violence and crime, and border agents can’t be as tough as they need to be because of feckless politicians — Democrats, mostly — who don’t believe in borders.

What you can’t tell by listening to Trump is that “catch and release” doesn’t refer to a single policy practiced by the government. It’s a label that gets applied to a handful of different practices that all have the same result: The US keeps trying to deport an immigrant, but it releases her from physical custody.

Deporting someone isn’t as simple as spotting her, handcuffing her, and putting her on a plane. Immigrants have to be issued an official order of removal — and usually, it needs to be issued by an immigration judge. Immigration courts are so backlogged right now that a wait to see a judge could take weeks; if an immigrant actually has an argument to be allowed to stay in the United States, it could be years before the case is resolved.

If the government decides, at any point, that it doesn’t need to keep the immigrant in detention through that whole process — if it decides not to detain her at all because she’s likely to show up to court anyway, if it has to release her because of a court order, or if it simply doesn’t have the resources to keep her in detention for years — it can theoretically be accused of practicing “catch and release.”

During the George W. Bush administration, Border Patrol agents routinely did this when they caught immigrants crossing the US-Mexico border from Central America or other non-Mexican countries. They’d open up an official deportation case in an immigration court, then release the immigrant to show up at his next court date. But as the Bush administration got serious about a border crackdown during its second term, it started keeping all immigrants caught at the border in detention as a matter of course; a 2006 press release from the Department of Homeland Security trumpets, “DHS Secretary Announces End to ‘Catch and Release’ on Southern Border.”

Toward the end of the Obama administration, Border Patrol agents grumbled that President Obama was “bringing back ‘catch and release,’” because DHS instructed agents not to prioritize the arrest and detention of immigrants unless they had criminal records or had recently crossed the border. But those instructions were explicitly designed to apply only to immigrants caught by Border Patrol (and Immigration and Customs Enforcement) who were already living in the US — not to force them to release immigrants caught crossing from Mexico.

The Trump administration got rid of those restrictions during Trump’s first week in office. At the same time, it tried to mandate that all immigrants caught crossing into the US be kept in detention while their cases were resolved. But while the Trump administration could expand the number of people getting sucked up by immigration enforcement, it couldn’t always control what happened to them once they were put into the deportation process.

“Catch and release” mostly only happens to children, families, and asylum seekers

Over the past few years, an increasing number of people caught at the US-Mexico border have fallen into categories that get particular legal protections: They’re children or teenagers traveling alone from Central America, or they’re families traveling together, and/or they want to seek asylum to flee deadly peril in their home countries.

While border crossings overall are still way lower than they were before the Great Recession, these groups make up a bigger share of immigrants getting apprehended. And spectacular news stories like the child migrant crisis of 2014, or the 1,200-member “caravan” traveling through Mexico last week, call attention to the fact that some people are still crossing into the US — and that they can’t, for various reasons, be summarily detained and deported.

The legal protections that prevent that are what the Trump administration is calling “catch and release” now.

Unaccompanied alien children from countries other than Mexico. Federal law treats people crossing into the US differently if they’re under 18 and coming without an adult relative — essentially, instead of thinking of them primarily as people who violated immigration law, it thinks of them primarily as potential victims of human trafficking. When an unaccompanied child comes to the US from a country other than Canada or Mexico, they’re sent to the Department of Health and Human Services for temporary foster custody and are ultimately (usually) placed with a relative in the US.

A law passed in 2008, the Trafficking Victims Protection Reauthorization Act (TVPRA), made it easier for these children to apply for and qualify for legal status in the US. (It also created a separate, quicker screening process for Mexican children caught at the border — which has been criticized by international observers for not protecting trafficking victims.)

This appears to be one of the “Obama” laws Trump is referring to (though it was signed into law by George W. Bush).

Families apprehended together. Children who come to the US with a parent aren’t subject to the anti-trafficking law, but they’re still supposed to get added protections because they’re children. Ever since the 1990s, the federal government’s use of immigration detention on children and families has been overseen by the federal courts (thanks to a settlement called the “Flores settlement”), with strict restrictions that keep most detention facilities and jails from being used to house families.

In 2014, when the Obama administration attempted to expand the widespread detention of families in response to the “border crisis,” the federal courts stepped in and ruled that under the Flores settlement, families couldn’t be kept in detention for longer than 20 days.

People claiming a fear of persecution. International law prevents the US from sending people back to places where they will be persecuted and could be killed.

In practice, right now, it means that any immigrant who’s apprehended at the border is supposed to be asked whether they fear persecution in their home countries — and that if they say yes, they’re automatically sent to an interview with an asylum officer. If the asylum officer deems the immigrant’s fear to be “credible,” she’s put into standard immigration court proceedings to plead her asylum case more fully. (Human rights groups claim that some Customs and Border Protection officials have refused to send immigrants to interviews with asylum officers.)

Immigrants almost always get deemed “credible” in these interviews — though the rate has declined slightly under a year of Trump, from about 80 percent to about 75. Not all of these immigrants end up getting asylum, but they get a chance to try. And often, those immigrants get released (either because the government decides to release them or the immigration judge says they can be released on bond) while their asylum cases are pending.

Trump says that once immigrants who enter the US get released, they never show up to their court dates. That’s not true — but the problem of people “absconding” is nonetheless real.

In fiscal year 2017, the last year for which data is available, about 40,000 deportation orders were issued in absentia — that is, to immigrants who hadn’t shown up. Most immigrants, however, did show up to their court dates; 60,000 immigrants showed up only to get deported. Thousands more actually won their cases, and then there are who knows how many immigrants who showed up to ask for (and get) more time to put their cases together.

But that’s still 40,000 people the Trump administration thinks shouldn’t have been in the US to begin with. And the rhetoric from Trump officials like Attorney General Jeff Sessions — who in December accused “dirty immigration lawyers” of deliberately jamming immigration courts with flimsy asylum claims — indicates they don’t think many of the rest should be in the country either. The best way to keep immigrants from getting in touch with lawyers (“dirty” or otherwise) and the best way to keep them from absconding are the same: deport them as quickly as possible and keep them detained in the meantime.

The White House says Trump is already ending “catch and release.” But it’s also saying Congress needs to finish the job.

When Trump took office, these groups of immigrants all but stopped coming into the US. Border apprehensions in the first few months of 2017 were at almost unthinkably low levels. Many experts concluded that fear of what Trump’s government might do to immigrants had chilled families and asylum seekers from trying to come to the US.

That’s exactly the outcome the Trump administration wanted. But it didn’t last. Because while the Trump administration tried to release as few immigrants as possible, it’s run into the laws that guarantee special legal protections for the groups that make up many border crossers.

The Trump administration has attempted to deal with “catch and release” by separating some families at the border, putting the parents into detention as adults and sending the children to the Department of Health and Human Services. Meanwhile, according to immigration lawyers near the border, some immigrants who try to claim asylum are getting prosecuted in federal court for illegal entry rather than getting the chance to prove their asylum cases. (The federal government denies this and says that upon expressing a fear of persecution, all immigrants are referred to an asylum officer.)

They’re still trying to tighten the screws as much as possible. Before Friday’s memo from Trump, Sessions told US attorneys that they now have to prosecute every single illegal entry case referred to them by DHS, regardless of circumstances (such as whether an immigrant came with children, or whether she’s seeking asylum). That’s likely to take up even more of federal prosecutors’ time on what’s already the most commonly charged federal offense.

White House officials say that Congress ultimately needs to close the “loopholes” that prevent across-the-board mass detention:

Amend the anti-trafficking TVPRA bill so that the expedited process for screening Mexican children also applies to children from other countries

Override the Flores settlement so that families can be kept in traditional immigration detention facilities

Change the standard for a “credible fear” screening so that the “credibility” assessment is different from the “fear” assessment — in other words, if the asylum officer thinks there’s something wrong with the immigrant’s story, they should be allowed to flunk the immigrant and put them back on the deportation track

Some White House officials appear to see the president’s new fascination with “catch and release” as an opportunity to pressure Congress to make these changes. With the nation’s attention focused on the border, one senior administration official said Wednesday, “I’m not sure how long” Democrats can maintain a filibuster.

The measures above probably wouldn’t stop immigration judges from ordering some immigrants released while their cases were pending. In other words, it wouldn’t end “catch and release” entirely. But it would severely restrict it.

Trump, as is his wont, treats “catch and release“ as an act of obvious stupidity or willful blindness — or even an act of sabotage, with Democrats serving as a fifth column to aid and abet the invading horde. But the “loopholes” aren’t accidents. They were placed there because Congress and the courts decided that children and families shouldn’t be detained indefinitely, and that those fleeing persecution should be treated as potential victims rather than presumed criminals. They decided, in other words, that some people deserve particular mercy: to be caught and processed but, in the meantime, released.