Moises Castillo / AP

The images are the same: Men, women, and children huddling together, exhausted from hours of walking, finding any space to rest their eyes—cement floors in a shelter, grass in a parking lot. The stories are also familiar: Some fear gangs and death threats, others flee rape and domestic violence. Just months after a caravan of migrants bound for the U.S. gained national attention in April, another group, estimated at 2,000, is in Guatemala heading north. It’s yet another demonstration of how even harsh attempts to deter migrants from making the journey to the U.S.-Mexico border, including separating parents and children, often fail.

On Tuesday morning, Donald Trump threatened to cut aid to Honduras, a country plagued by violence, if it doesn’t stop the caravan that left from San Pedro Sula. “The United States has strongly informed the President of Honduras that if the large Caravan of people heading to the U.S. is not stopped and brought back to Honduras, no more money or aid will be given to Honduras, effective immediately,” he said on Twitter.

Trump made a similar threat in April. It’s one of many attempts by the administration to stem the flow of illegal immigration. Earlier this year, the administration announced its “zero tolerance” policy that led to families being separated. More than 200 children remain in federal custody after more than 2,500 children were separated from their parents from April to June, before Trump halted the program.

This zero-tolerance policy sparked outrage across the country. But the message the administration was trying to send to immigrants was clear: Come at your own risk. In unveiling the policy in April, Attorney General Jeff Sessions said: “To those who wish to challenge the Trump administration’s commitment to public safety, national security, and the rule of law, I warn you: Illegally entering this country will not be rewarded, but will instead be met with the full prosecutorial powers of the Department of Justice.” In an interview with NPR shortly after, John Kelly, the White House chief of staff, cited deterrence as a reason for the policy. “They’re coming here for a reason. And I sympathize with the reason. But the laws are the laws. But a big name of the game is deterrence,” he said.

On Sunday, Trump himself made the case for deterrence in a 60 Minutes interview. “When you don’t do separation, when you allow the parents [and children] to stay together, okay, when you allow that, then what happens is people are gonna pour into our country,” he said.

It isn’t the first time the U.S. has relied on a deterrence policy. Former President Barack Obama’s administration tried to prevent people from crossing the border through a number of tactics short of separating parents from their children, like family detention and running ads in Central America discouraging people from making the dangerous journey. But as evidence has shown again and again, these policies don’t always succeed, especially when people are fleeing dangerous conditions in their homeland.

Simply stated, deterrence policies “don’t work,” Rebecca Hamlin, an associate professor of legal studies at the University of Massachusetts at Amherst, told me in 2016, following new initiatives by the Obama administration to address Central American migrants. “They might work when someone’s only motivation to migrate is economic, but they really don’t work—and this is consistently found all over the world—when it comes to people who are fleeing what they believe to be potentially a life-or-death situation.”

The Center for American Progress, a left-leaning think tank, found in analyzing federal data that both family detention, as used during the Obama administration, and family separation, under Trump, are “ineffective deterrents.”

“We’ve certainly seen more than enough evidence of what conditions are like in places like Honduras and El Salvador that are pushing people experiencing high levels of gender-based violence or gang violence out of the countries,” said Philip Wolgin, the managing director for immigration policy at the Center for American Progress. “The analogy I’ve heard most often is: If the choice is sudden death or imminent certain death in your country, or going somewhere else with the possibility you might be detained or separated, you take the lesser of the two evils.”

The number of family apprehensions from January to June 2018, during Trump’s second year in office, was actually more than twice that during his first year in the White House, according to a Pew Research Center analysis of U.S. Customs and Border Protection data. In May, the first full month the family-separation policy was in effect, more than 9,000 family members were apprehended, up from around 1,500 in 2017. Since Trump signed an executive order ending family separations in June, apprehensions have continued to rise.

Still, the Trump administration appears to believe the zero-tolerance policy drove down the number of immigrants trying to enter the country illegally, according to documents obtained by CNN earlier this year. Homeland Security staff acknowledged in the document that results wouldn’t be “fully realized for 2–3 weeks following public messaging,” but added that “some migrants already underway may temporarily halt to determine the effects of the new policy.”

The senior White House adviser Stephen Miller also appears to believe that family separation kept migrants from traveling to the U.S.-Mexico border, The Washington Post reported. So much so that the White House is reportedly floating plans that could separate parents and children yet again. In the 60 Minutes interview, Trump refused to say whether he’d reinstitute his zero-tolerance policy. “What I can say is this: There are consequences from coming into a country, namely our country, illegally,” he said.

Most recently, the administration proposed modifying the Flores agreement, a 1997 consent decree that prohibits the detention of migrant children in unlicensed secure federal facilities for more than 20 days. Because the Obama administration refused to separate families, the Flores agreement effectively meant that most families apprehended at the border were processed, released, and told to return for an immigration hearing at a later date—a system Trump has ridiculed as “catch and release.” But any changes the Trump administration attempts to bring about with the Flores agreement are likely to be met with legal challenges.

As happened earlier this year, it’s possible that the number of people in the caravan making its way north will dwindle, but by happening again, it demonstrates that severe detention and separation policies simply don’t deter immigrants fleeing murder and mayhem from crossing the U.S. border.

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