“I think the idea from the Trump administration that you can somehow just stop people from coming by either threatening to cut off the aid—which basically goes to the government, not to the people that are fleeing—or by believing you can close off borders is not going to really address why people are very willing to get up from one day to the next, it seems, and travel north with the hope for a better life,” said Maureen Meyer, the director for Mexico and migrant rights at the Washington Office on Latin America, an advocacy organization.

A key aspect of the “zero tolerance” policy that greeted the April caravan’s arrival called for the prosecution of adults crossing the border illegally. After pleading guilty to illegal entry—which is a misdemeanor—migrants were sentenced to time served and, later, processed for deportation. But this was the problem: “Criminalizing” border crossing necessitated family separation—because children by law couldn’t be kept in federal jail.

Read: Trumpism, Realized

Attorney General Jeff Sessions described the situation at the time as “a crisis … that necessitates an escalated effort to prosecute those who choose to illegally cross our border.” Trump, under intense political pressure, eventually ended the policy, which had led to roughly 2,000 separated families, through an executive order in June. But even “zero tolerance” and family separation haven’t stemmed the flow of migrants from El Salvador, Honduras, and Guatemala.

After prosecuting those illegally crossing the border, Sessions sought in June to make it much harder for migrants to be granted asylum: He reversed an immigration-appeals-court ruling and said that domestic abuse and gang violence no longer qualified as grounds for asylum. The ruling immediately undercut the claims of many migrants from Latin America, where gang violence is endemic. The administration has also recently been floating a number of possible new policies aimed at deterring migrants, one of which would include forcing parents who cross the border illegally with their children to give them up to foster care or be detained together, according to media reports.

The goal is clear: to discourage migrants from coming to the United States. Former President Barack Obama also tried to stem the flow of migrants journeying to the U.S.-Mexico border with threats of detention. He, too, discovered that deterrence policies usually fail in the face of economic distress and violence.

To that end, in 2016, then–Secretary of State John Kerry announced a plan that, with the help of the United Nations, would identify people eligible for refugee status in El Salvador, Guatemala, and Honduras. Those who were fleeing imminent danger would be placed in Costa Rica for processing. The administration also expanded the Central American minors program to include siblings, parents, and caregivers accompanying minors.