Over the last two months, the Trump administration has forcibly taken about 2,000 children away from their parents at the U.S.-Mexico border and placed them in detention centers as a deterrent against illegal immigration. The new border policy has inspired outrage, nationwide protests, and a number of A.C.L.U. lawsuits, and even Donald Trump has said that this “horrible and cruel” practice must end.

“I hate the children being taken away,” Trump told reporters on Friday morning. “The Democrats have to change their law—that’s their law.”

But it’s not their law. In fact, it’s not a law at all.

Trump has been continuously citing an immigration and border-protection policy implemented by the Obama administration that placed hundreds of families in immigration detention centers at the height of the 2014 migrant crisis, when there was a surge in unaccompanied minors and women fleeing violence in Central America. In other cases, children would be separated from parents facing criminal prosecution, as they would not be able to accompany them into federal detention centers. But previous administrations made allowances for immigrants traveling with children—many of them seeking asylum in the U.S.—allowing the families to stay together while being processed. The Trump administration, however, has decided that all adults crossing the border must be criminally prosecuted, with no exceptions. The new “zero-tolerance” policy put in place by Attorney General Jeff Sessions in April requires that children are taken away from their parents and treated as unaccompanied minors, as if they tried to cross the border alone.

White House Chief of Staff John Kelly, when asked about the policy last month, referred to it as a “deterrent.” Critics say it is more akin to child abuse. There’s ample evidence that taking children from their parents at such young ages (many of them are younger than four) causes lasting developmental and emotional damage. “What we find from a neurobiological sense is that the circuitry in the brain that is a fear response can be actually harmed,” Dr. Lisa Fortuna, medical director for child and adolescent psychiatry at Boston Medical Center, told Business Insider. Putting children in a situation as traumatic as taking them away from their parents can make them more susceptible to behavioral problems like depression, anxiety, and P.T.S.D.

House Democratic leader Nancy Pelosi has called the policy “barbaric.” Sessions has described it as justice: “If you don’t like that, then don’t smuggle children over our border.”

The family-separation policy isn’t being used merely as a deterrent, however, but also as a bargaining chip, with imprisoned children as political hostages. Instead of ending the cruel policy, which he could do immediately, Trump has maintained family separation as leverage to force Democrats to accede to sweeping limits on immigration. As he tweeted Saturday morning, “Democrats can fix their forced family breakup at the Border by working with Republicans on new legislation, for a change!”

Trump doesn’t seem to be backing down, even after other Republicans have started to voice their doubts. House Speaker Paul Ryan said that he’s not comfortable with the policy, and Governor John Kasich tweeted on Friday, “Quit separating families. It’s that simple.”

“Before, their cases would have been dealt with as a family,” Megan McKenna, senior director of communications at the nonprofit Kids in Need of Defense (KIND), told Business Insider. “It’s a problem of the government’s own making.”