Jeh Charles Johnson served as secretary of homeland security from 2013 to 2017.

My wife and I spent Mother’s Day in 2014 at a U.S. Border Patrol center in McAllen, Tex. The facility had been built for single adults, but it looked like a crude day-care center flooded with children. In the midst of that flood, my eyes were drawn to one little girl sitting alone at a desk and being processed by a Border Patrol agent. I was struck by her long, black hair, which was beautiful despite the hot and dirty journey from Central America she just had completed. I asked her, “Why did you come here?” She replied: “I’m looking for my mother in the United States.” She began to cry, the translator began to cry, and I began to cry.

As I witness the Trump administration’s current practice of separating children from their parents at the border with Mexico, the image of that little girl and hundreds of other migrant women and children is fixed in my mind.

I hesitate to criticize my successors in office, who are burdened with the responsibility of keeping the U.S. homeland and its borders secure. I hesitate to cast doubt on the hard work of those who once worked for me in the Department of Homeland Security. But when it comes to certain offensive and wrongheaded government policies, those of us with a public voice and who understand the issue cannot stay silent.

The current “zero tolerance” deterrent policy, resulting in the separation of 2,000 innocent migrant children from their parents, is immoral and un-American. Beyond that, the policy will in the long run prove to be ineffective.

Experience teaches (as career personnel at DHS know) that widely publicized changes in immigration-enforcement policy may cause sharp downturns in the level of illegal migration in the short term, but migration patterns then revert to their higher, traditional levels in the long term so long as underlying conditions persist. I learned this hard lesson while in office; the Trump administration is learning the lesson now.

In my three years as secretary of homeland security, the government deported, repatriated or returned about 1 million people in the enforcement of the immigration laws. To address illegal migration, I considered and directed a number of very unattractive measures. When illegal migration spiked in 2014, we expanded our family detention capability, a move that I freely admit was controversial (even though, unlike the Trump administration’s approach, it kept children with their parents). Our efforts brought mixed results. In 2015, we saw a sharp decrease in apprehensions on the southern border to the lowest levels since 1972. But in fiscal 2016 the numbers increased again.

It is basic human instinct to save yourself and your family by fleeing a burning building. So long as the powerful “push factors” of poverty and violence in Guatemala, Honduras and El Salvador persist, the United States will continue to wrestle with the problem of illegal migration on the border with Mexico.

Further, the current policy is unsustainable. We cannot continue to flood the federal courts across the Southwest with thousands of new migrants per month to extract assembly-line guilty pleas from them, while also filling facilities for holding migrant adults, children and families. These facilities are already at full capacity, and the policy is blowing a hole through the budgets of DHS, the Justice Department and the Department of Health and Human Services. Meanwhile, other vital law enforcement and homeland-security priorities are being overlooked.

The answer to the underlying problem is twofold. First, send more aid to Central America. In 2016, Congress started down this road by appropriating $750 million in assistance for Guatemala, Honduras and El Salvador. In subsequent years that level of support has fallen off. Congress must do more. Second, encourage the neighboring countries in the region — Mexico, Panama, Costa Rica and Belize — to develop their own systems, as alternatives to the United States, for accepting Central American refugees and asylum seekers. This is not politics; it is basic common sense.

It is also common sense that children belong with their parents. Americans should demand that their government end its current cruel, disastrous policy on the southern border.