The U.S. government has deported hundreds of migrant parents without their children in the aftermath of President Trump’s now-defunct family separation policy. But now administration officials are arguing that it’s the responsibility of the American Civil Liberties Union, not the federal government, to find those deported mothers and fathers.

Justice Department lawyers wrote in a court filing Thursday that the ACLU should use its “considerable resources,” its network of advocacy groups, and information from the government to locate parents removed to foreign countries. The Trump administration added, however, that the State Department has made contact with foreign governments to assist in facilitating family reunions.

In Thursday’s court filing, a joint status report requested by Judge Dana M. Sabraw of the U.S. District Court for the Southern District of California, both the Trump administration and the ACLU laid out their plans for the continued reunification of families. The report gives a sense of the complex challenges ahead for both U.S. officials and immigration lawyers in locating the parents who are no longer in the United States.

In the six weeks before President Trump reversed his “zero-tolerance” policy at the border, immigration officials removed more than 2,500 children from their parents and sent them to government shelters. Sabraw, a Republican appointee, ordered the government to return the children as quickly as possible, setting a deadline of late last month.

The administration has since reunited more than 1,800 children with their parents, but hundreds of children remain in government shelters because their parents have criminal records, their cases remain under review or their parents are outside the country. More than 450 mothers and fathers have been deported without their children.

ACLU lawyers pushed back against the Trump administration’s demands to find the deported parents, saying that they will do “whatever they can” but that the government must bear the ultimate burden.

“Not only was it the government’s unconstitutional separation practice that led to this crisis, but the United States Government has far more resources than any group of NGOs,” ACLU lawyers wrote in the court filing. “Plaintiffs therefore hope that the Government will take significant and prompt steps to find the parents on their own.”

The ACLU wrote that “there is no blueprint for finding deported parents,” who are scattered in various cities across Central America and who, in many cases, left behind minimal address information.

“It often takes a degree of detective work and investigation in order to track down the most up-to date contact information for deported individuals,” the ACLU wrote. “In addition, because deported parents may be hiding from persecutors, it is often not easy to track down exactly where they may be located. This means that every possible lead must be pursued.”

The government on Tuesday provided a list of available addresses, but much of this information was “not helpful,” the ACLU said. Some locations are listed as “In DHS Custody,” “failed to provide” or the addresses of detention centers in the United States.

About 120 deported parents, more than a quarter of the total number removed without their children, have no “potentially viable” addresses in the government’s database, the ACLU said. Even among the viable addresses, some include only a city name or are listed as “calle sin nombre,” or “street without a name.” In many parts of Central America, addresses are often listed not as street names and house numbers but as distances from landmarks, such as a local church.

For these reasons, phone numbers are far more useful than addresses for making contact with deported parents, the ACLU said. It argued that the government has had access to possible phone numbers of some of the deported parents but failed to use the contact information ahead of deadlines assigned by Sabraw. ACLU lawyers asked the government for “as much information as possible, as quickly as possible.”

“As the Court is aware, the children with deported parents are suffering as much, if not more, than the children whose parents remained in the United States,” the ACLU wrote.

Once a parent is located, the government asked that the parent or his or her attorney provide written confirmation that the parent wants to reunite with his or her child, as opposed to waiving that right. Once a parent chooses to reunite with a child, the ACLU asked that the government reunite the family within seven days.

The ACLU lawyers also asked the government to arrange travel documents and pay for airfare to reunite children with their deported parents.

The two parties filed Thursday’s joint report ahead of a status conference with the federal judge on Friday afternoon.

Trump administration officials faced intense criticism from Democrats over the migrant family separations during a Senate testimony Tuesday. Some government officials pushed back, defending the rationale for the separation policy. One senior Immigration and Customs Enforcement official, Matthew Albence, likened family detention centers to “summer camp.”

But when Sen. Richard Blumenthal (D-Conn.) dared five Trump officials to say the zero-tolerance border strategy was a success, not one raised a hand.

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