What happened
Attorney General Jeff Sessions's April 2018 memorandum directed federal prosecutors to pursue criminal charges against all adults who crossed the border without authorization, with no exception for those travelling with children — since children cannot be held in criminal custody with a parent, this made separation an automatic, foreseen consequence of the policy rather than an unintended side effect.
More than 5,500 children were separated from their parents under the policy, which ran officially from April to June 2018 but continued in practice for at least eighteen months afterward, separating an additional estimated 1,100 families between mid-2018 and the end of 2019.
The government had built no centralised system to track which child belonged to which parent once they were sent to separate facilities and, in many cases, separate parts of the country. By the court-ordered reunification deadline, more than 900 parents had not been reunited with their children — 463 of whom had already been deported without them. Years after the policy officially ended, some of the nearly 3,000 children taken during the zero-tolerance period had still not been reunited with their families.