When President Donald Trump signed an executive order ending the separation of children from their families at the border, it did not end the crisis in Central America. Nor should it relieve our moral anguish at seeing the poorest and most vulnerable treated in ways that are fundamentally at odds with our nation’s values.

The moment also calls for a renewed focus on the so-called Northern Triangle of Central America — the countries of El Salvador, Guatemala and Honduras, which together represent the overwhelming source of migrants crossing our southern border. Unless we address the root causes driving migration from this region, any solutions focused solely on border protection and immigration enforcement will be insufficient.

This is terrain I know all too well. In 2014, President Barack Obama asked me to lead the international response to the surge of migrants that ultimately resulted in 68,000 unaccompanied children from Central America crossing into the United States. That summer, I met with Central American leaders in Guatemala to chart a plan to reduce migration, as well as to make it clear that undocumented migration was risky, dangerous and offered scant hope of legal status or citizenship.

It soon became evident that migration from Central America could not be resolved merely by stronger enforcement at the U.S. border, let alone by building a wall. Instead, we needed to tackle the drivers of migration: crime, violence, corruption and lack of opportunity. We knew the cost of investing in a secure and prosperous Central America was modest compared with the cost of allowing violence and poverty to fester.

Following intensive negotiations between the Obama administration and the Northern Triangle presidents, Congress provided $750 million in 2016 to fund a whole-of-government effort to effect deep and lasting change in Central America. Because Central American governments had long been perceived — with good reason — as corrupt, inept and incapable of delivering basic services to their citizens, I supported Congress in tying the aid package to concrete commitments by regional governments to clean up their police, increase tax collection, fight corruption and create the opportunities necessary to convince would-be migrants to remain in their countries.

In turn, the countries pledged billions of dollars in their own money to deliver on the promise of prosperity, security and governance. We also implemented new programs to help those in immediate danger by allowing them to apply for asylum without the dangerous journey to the U.S.

By the end of the Obama administration, we began to see results. The murder rate in Honduras dropped by a third since its peak in 2011. Guatemala improved its tax collection and made inroads against corruption, renewing a vital U.N.-backed anticorruption commission until 2019. El Salvador was aggressively targeting the financial networks of transnational criminal organizations. Meanwhile, energy cooperation in the region extended access to electricity in countries such as Honduras, where as much as 12 percent of the population is still unconnected.

But this progress required face-to-face diplomacy to convince leaders of these nations to act against their own political instincts and to establish clear benchmarks that demonstrated a real will to change. We knew that sustained, bipartisan U.S. engagement — and, yes, pressure — were necessary for progress.

The Trump administration came into office determined to slash aid to Central America, and only partly succeeded because of the pushback from engaged members of Congress on both sides of the aisle. Still, U.S. assistance has fallen by nearly 20 percent, from $750 million in 2016 to $615 million this year.

After a promising early conference in Miami on security and prosperity in Central America in June 2017, attended by Vice President Mike Pence and several Cabinet secretaries, the three Northern Triangle presidents have not met jointly with a senior U.S. official in well over a year. By contrast, I met with them three times during my final year in office. Occasional bilateral visits such as the one earlier this month between Secretary of State Mike Pompeo and Honduran President Juan Orlando Hernández cannot replace a comprehensive regional approach to reduce the drivers of migration.

Fortunately, there is still time to build on the policy that emerged from the last major migration crisis in 2014 — a policy modeled in part on the successful, bipartisan approach to Plan Colombia. When the vice president travels this week to Guatemala, the president should send him with a mandate to revive the intense diplomatic and aid efforts that gave rise to the Alliance for Prosperity, and opened a window of hope for the most besieged countries in our hemisphere.

We can both strengthen U.S. border security and treat migrants arriving from Central America with dignity and decency instead of cruelty and callousness. But their overwhelming desire to flee their countries and risk everything to enter the U.S. shows that their governments are still failing them. This migration will only continue unless we keep up the pressure and provide the support to make the Northern Triangle of Central America a prosperous and secure place to call home.

Joseph R. Biden Jr. was vice president of the United States from 2009 to 2017. He wrote this article for the Washington Post.