President Donald Trump is screaming mad at his homeland security secretary, Kirstjen Nielsen, for failing to stop people from coming to the US without papers.

According to reports in the New York Times and Washington Post, Trump went on a half-hour rant at Nielsen during a recent Cabinet meeting — an unusually long tantrum even for him (and one that reportedly made other officials in the room uncomfortable). The Times reported that Nielsen wrote a resignation letter but hadn’t yet decided to submit it; the Post’s reporting says no such letter was drafted.

Trump reportedly blames Nielsen for the fact that, despite the Trump administration’s renewed effort to crack down on families, children, and asylum seekers crossing into the US in the name of ending “catch and release,” 50,000 people without papers came into federal custody at the border in both March and April.

Nielsen, as well as Attorney General Jeff Sessions, apparently tried to explain to the president that the federal government is constrained in what it can do by the law, but Trump reportedly wasn’t having it. “We need to shut it down,” he yelled at Nielsen at one point, per the Post report. “We’re closed.”

Yelling at people is a management tactic for President Trump; sometimes his anger inspires long-held grudges, but sometimes it dissipates once he’s gotten it off his chest. But he’s spent the past month in an apparent panic about the border, and his outburst at Nielsen shows it isn’t going away.

The president’s tantrum is totally divorced from policy reality: The government can’t “shut it down,” and Nielsen and Sessions appear to be working aggressively to do what they can to crack down at the border. But Trump’s panic is the inevitable consequence of treating the current situation at the border as an unprecedented crisis — which Nielsen’s DHS, as well as the White House, has made a concerted effort to do.

Trump thought the fact of his existence would keep people from coming into the US

Donald Trump’s inauguration really does appear to have deterred a lot of people from trying to enter the US without papers.

At least for a while.

In the first few months of 2017, apprehensions of unauthorized immigrants by Border Patrol (the way the government measures how many people are crossing illegally into the US) plummeted to unprecedented levels. The fact that the biggest change from December 2016 to January 2017 was the inauguration of President Trump — and that the last few months of the Obama administration had seen higher-than-usual levels of apprehensions, perhaps from people trying to beat the new president to the US — led a lot of analysts to conclude that Trump’s unforgiving rhetoric on immigration had created so much worry about how immigrants entering the US would be treated that many people decided it wasn’t worth the risk.

But the effect didn’t last. In summer 2017, Border Patrol agents started warning that numbers were creeping back up. They stayed level through fall and winter — as apprehensions usually fall. And in March, they started spiking.

Trump’s tantrum at Nielsen was reportedly sparked by the fact that over both March and April, more than 50,000 people without papers came into the custody of federal officials at the border. That’s higher than the past few years, but it’s still lower than apprehensions in 2013 or 2014 — and still way lower than a typical spring under the Bush administration, before a combination of increased enforcement and the Great Recession cut border crossings to a fraction of what they once were.

Contrary to what the Trump administration claims, however, fewer than 50,000 people a month have been caught trying to enter the US illegally. That number includes people who cross illegally and are caught by US Border Patrol agents, as well as people without papers who present themselves at ports of entry to Customs and Border Protection officials — often to seek asylum.

It is perfectly legal to present oneself for asylum at a port of entry, and in fact, it’s what the Trump administration claims it’s encouraging immigrants to do. The purpose of the recent effort to prosecute all adults caught by Border Patrol in federal court, according to Attorney General Jeff Sessions and acting Immigration and Customs Enforcement (ICE) Director Tom Homan, is to get them to go through ports of entry instead. But at the same time, they’re counting those people as part of the crisis.

If you believe that people coming into the US without papers are an urgent threat to national security regardless of who those people are, why they are coming, or how many of them there are, the crisis approach makes sense. But even by that standard, the United States has been in a constant state of crisis for the past three decades. It’s impossible to look at the historical context and argue that what’s happening is unusually bad.

Everyone but Trump appears to understand you can’t literally just shut down the border

People both within and outside the government understood a year ago that the absurdly quiet border of Trump’s first months wouldn’t last. They knew that people make decisions about whether to migrate based on what they know about the potential outcome — and that without policy changes, all the tough talk in the world wouldn’t drown out information making it back to immigrants’ home countries that it was still a good bet to come to the US.

And while the president of the United States appears to believe that he can just shut down the border with a snap of his fingers, that is not in fact the case.

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 — which is to say, they can’t be summarily denied entrance to the US or deported without violating federal and/or international law. 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.

Because 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 now calling “catch and release.”

Nielsen’s DHS and Sessions’s Department of Justice are moving aggressively to change executive branch policy to deal more harshly with asylum seekers and families, requiring criminal prosecution (which entails separating parents from children) for anyone caught by Border Patrol and moving to expand immigration detention. Statistics show that immigration judges are denying more asylum claims in fiscal year 2018 so far.

But even in the executive branch, policy change takes time — at least if it’s going to be done with even a minimum of care.

That’s especially true in this case because the administration doesn’t have much room to crack down without violating a federal court settlement guiding the treatment of families; federal statutes guiding the treatment of unaccompanied children and asylum seekers; and international law preventing the US from sending people back to countries where their lives are in peril.

Administration officials have known this from the beginning. From the minute the Central American “caravan” first caught Trump’s attention last month, officials have said publicly that their real goal is to pressure Congress to write a new law giving them more powers. With the nation’s attention focused on the border, one senior administration official said on an April 7 press call, “I’m not sure how long” Democrats can maintain a filibuster.

Officials appear to have overestimated their ability to control who would be blamed for the panic, and on whom the pressure would fall. Their efforts to portray the current situation at the border as a crisis have succeeded — they’ve panicked the president of the United States. And he simply doesn’t believe that the problem can’t be solved without the cooperation of recalcitrant Democrats.

The Trump administration is the dog that caught the car

Trump is paying attention to the border because he thinks it’s a crisis. And initially, administration officials appeared to welcome this attention because it created the space for policy change. The proposals that officials are pushing on Congress now were part of the administration’s demands during the congressional debate over the future of the 690,000 immigrants covered by the Deferred Action for Childhood Arrivals (DACA) program — and as the debate wore on, it became increasingly clear that Nielsen and others saw changes to asylum and family policy at the border as an urgent priority. But they didn’t rise to that level for Trump himself, and so they got swamped by everything else the president wanted to pile into a DACA deal.

But Trump’s attention is a double-edged sword. It too easily erupts into venting. It can’t be easily calmed by policy explanation. And because the president’s fixations drive his off-the-cuff statements, which in turn drive the news cycle, the crisis has the potential to feed on itself for a long time.

As irrational as Trump often appears, though, he’s politically not wrong.

The problem with using a crisis to rise to power is that once you’re in power, the crisis is yours to solve — and your responsibility is commensurate with the size of the crisis.

If you run for president by claiming, contrary to all available facts, that the US “doesn’t have” a border anymore, once you’re elected, you’re on the hook for showing big changes. The fact that you were vastly overstating the size of the problem before you were elected just means you made it seem much easier to solve.

Keeping people from Central America from coming to the US without papers — which is, manifestly, the Trump administration’s goal — is a hard policy problem. There is a reason that despite a fairly hawkish attitude toward Central American families from the Obama administration (and enthusiastic cooperation from the Mexican government), it has not been solved yet.

Trump, who appears to have no understanding of policy, may not be aware of this. Nielsen and other officials absolutely are. They can try to blame Democrats in Congress, less-than-cooperative state governments, and (riskily) the Mexican government. But at a certain point, Trump knows the truth: that once you decide this is a capital-P Problem, it is on you to find a way to declare it fixed.