What does the Flores case have to do with this?

The long-running class-action litigation over the treatment of children in immigration custody ended with a 1997 consent decree known as the Flores settlement. Under it, the government has been obligated to release children from immigration detention to relatives or, if none can be found, to a licensed program within about three to five days. If that is impossible, they must be held in the “least restrictive” setting appropriate to their age and needs.

In the second term of the Obama administration, amid a surge of migrants, the administration adopted a policy of detaining families headed by women together while their cases were processed. After those conditions were challenged in court, Judge Dolly M. Gee of Federal District Court for the Central District of California ruled that the Flores settlement terms also applied to accompanied minors, so holding children with their mothers in indefinite immigration detention was unlawful.

How much can Trump do without court permission?

The most important part of Mr. Trump’s order set in motion a request to get a court to approve holding families together for longer than 20 days. The order directs Mr. Sessions to promptly ask a federal court to “modify” the consent agreement in a manner that would permit the Department of Homeland Security to hold families together throughout immigration court proceedings. At his press briefing, Mr. Hamilton said that unless Congress acted sooner to change the law, it would be up to Judge Gee to decide whether the administration could keep families together.

What happens to the children already separated?

The administration initially said it would not try to reunite children and parents who were separated at the border under the zero-tolerance policy, according to Kenneth Wolfe, a spokesman for the Health and Human Services Department.

But the agency retreated later Wednesday evening, saying that “it is still very early, and we are awaiting further guidance on the matter.”

“Reunification is always the goal,” said Brian Marriott, the senior director of communications for the agency, noting that the department was working toward that for children affected by the president’s policy.

That statement left open the possibility, though, that the children could be reunited with relatives or “appropriate” sponsors in the United States, not necessarily the parent they were separated from at the border.