It may be hard to believe that this is happening in the United States in 2018, that hundreds of children are being snatched from their parents, frequently under false pretenses, often screaming, and placed in vast warehouselike centers like the former Walmart in Brownsville, Tex., where nearly 1,500 boys now spend their days. The parents often don’t know where their children are, or when they will see them again.

In 2014 the Obama administration detained hundreds of families and unaccompanied minors crossing the border, a practice that the federal courts quickly curtailed. But separating families as a matter of unofficial policy is something new and malicious, a function of President Trump’s obsession with undocumented immigrants. This spring, the administration ordered that everyone caught crossing illegally into the United States be prosecuted. And since children cannot accompany grown-ups to jail, people who had crossed illegally with children had their children taken away. Hundreds upon hundreds of children, of all ages, creating a new industry in mass shelters.

The United Nations human rights office called this new practice a serious violation of the rights of children and demanded an immediate halt. Catholic bishops denounced it as immoral. The American Psychological Association warned that the separations threatened the mental and physical health of the children. All to no avail.

The administration has come back with a mix of just-following-orders and falsehoods. The Department of Homeland Security said it had no policy for separating families; it was just catching criminals. President Trump feigned sympathy for the separations but claimed he was the victim of “bad legislation passed by the Democrats,” which nobody could find. Only John Kelly, the White House chief of staff, offered what appeared to be a plausible, if shocking, explanation: that separating parents from their children could be a “tough deterrent.”