The Flores settlement required immigration officials to “place each detained minor in the least restrictive setting appropriate” — for example, providing food, water and toilets. The government also agreed to release immigrant children “without unnecessary delay” under an established preference ranking for custody.

After a surge of families from Central America began arriving at the United States’ southwestern border in 2014, the Obama administration opened family detention centers. That prompted more lawsuits, which argued that doing so had breached the Flores settlement by not releasing children swiftly.

In 2016, the Ninth Circuit of Appeals ruled that the Flores settlement “unambiguously applies both to minors who are accompanied and unaccompanied by their parents.” It also overturned a Federal District Court’s decision that the government must also release the parents.

Attorney General Jeff Sessions announced a “zero tolerance” policy in April, stating that “our goal is to prosecute every case that is brought to us” — thus leading to the detention of migrant parents.

In other words, without the Trump administration’s new enforcement policy, the Flores settlement — and subsequent rulings clarifying its scope — alone would not have caused family separation at the border. As The New York Times reported last month:

Spurred on by the president, Attorney General Jeff Sessions last month announced a “zero tolerance” policy in which people who cross the border illegally are to be subject to criminal prosecution. On Tuesday, the administration officials argued that the two directives, taken together, essentially left them with no option other than to take children from their parents at the border.

Under Flores, the government has three options: releasing families together, passing a law that would allow for family detention or breaking up the families. The Trump administration has so far chosen the third option.

Source: Flores settlement text, Ninth Circuit of Appeals, The New York Times, Congressional Research Service, office of Representative Paul D. Ryan