Since migrant children cannot legally be held in federal criminal detention facilities, they must be separated from their parents while the adults are prosecuted. As a result, the rise in unlawful entry prosecutions has led to a related spike in the number of family separations at the border.

For example, more than 650 migrant children were separated from their parents during a two-week period in May, immigration officials told Congress on May 23.

The zero-tolerance policy has drawn blowback from Democrats and immigration activists, who used images of migrant children in detention centers to paint the Trump administration’s approach as needless and cruel. The administration has pushed back, arguing that separating migrant families while adults are prosecuted for unlawful entry is a needed deterrent that will reverse the rising tide of illegal immigration, particularly by people traveling in family units.

Under the new policy, migrant children separated from their parents are treated as if they had arrived on their own. That means they are referred to the Office of Refugee Resettlement (ORR), the agency within the Department of Health and Human Services (HHS) charged with caring for unaccompanied alien minors. ORR then tries to locate to an adult sponsor in the U.S. if one is available, or, failing that, places the migrant child in a government-contracted shelter.

By contrast, the Obama administration typically detained families together in administrative immigration detention facilities, often releasing them with a notice to appear in court because of limited bed space. That approach was widely criticized by immigration hawks, who said it created an incentive for further illegal immigration.

It remains to be seen if the zero-tolerance policy will stanch the flow of illegal immigration by children and family units, which has grown steadily since falling to historic lows in the early months of Trump’s presidency. What is clear is that the recent spike in family separations is largely the result of the Trump administration’s own prosecution policy, not any specific piece of legislation.

Laws on the books

When Trump blamed family separation on “bad legislation” by Democrats, he might have been referring to the 2008 Trafficking Victims Protection Reauthorization Act (TVPRA).

Passed by a bipartisan majority in Congress and signed into law by former President George W. Bush, TVPRA strengthened anti-human trafficking laws and established certain procedures for dealing with alien children in the U.S. The law requires immigration authorities to transfer unaccompanied minor children to HHS for care and processing, part of which entails guaranteeing to the “greatest extent practicable” pro bono legal counsel.

The TVPRA also codified parts of a Supreme Court–ordered settlement from 1997 known as the Flores consent decree. Flores requires the government to release unaccompanied alien children from immigration detention within 72 hours to the “least restrictive” setting possible — usually parents, relatives or ORR-licensed shelters.

Subsequent federal court rulings have found the Flores settlement applies to all alien children — those who arrived in the U.S. alone and those who were brought by adult relatives. The courts have also ruled that families cannot be detained in facilities that are not licensed child care centers for over 20 days.

The Trump administration refers to TVPRA and Flores as “loopholes” that invite more illegal immigration and force authorities to practice catch-and-release enforcement. Sessions and DHS Secretary Kirstjen Nielsen have called on Congress to change the policy to make it easier to deport Central American minors and keep families in immigration detention while they go through immigration court proceedings.