WASHINGTON — Advocates for immigrants say they still have not found the parents of 545 minors who were separated from their families starting three years ago during President Trump’s immigration crackdown at the U.S.-Mexico border.

The 545 children are among more than 1,500 who were separated from their parents as far back as July 1, 2017, and they include cases that were part of a pilot immigration program at the time and were not immediately disclosed to the federal judge who ordered the families reunited in June 2018, said American Civil Liberties Union lawyer Lee Gelernt.

More than two-thirds of the minors are from Central America, and the children are believed to be with sponsors or other family members in the United States.

“Unfortunately, there’s an enormous amount of work yet to be done to find these families – work that will be difficult, but we are committed to doing,” Gelernt said after filing information about the children with the federal court on Tuesday. “Not only are we still looking for hundreds of families, but we would have never even known about these families if the Trump administration had its way.”

Department of Homeland Security officials said Wednesday that the government has been working to reunite the children with their families but has found in some cases that parents do not want to claim them, a move that allows the children to remain in the United States. Justice Department lawyers have said in court filings that most of the separated children already have been released to parents or legal guardians.

“DHS has taken every step to facilitate the reunification of these families where the parents wanted such reunification to occur,” said DHS spokesman Chase Jennings.

Health and Human Services officials confirmed Wednesday that all of the 545 minors were “appropriately discharged” from its shelters – to a legal guardian or a parent – before June 2018, when the judge ordered the reunifications.

The ACLU has demanded the names of all separated parents and children and wants to confirm all reunifications. The organization, which filed the lawsuit that led to the judge’s order to reunite the families, estimates that as many as 5,400 children have been separated from their families since Trump took office.

More than half were split up from May to June in 2018, when the DHS and the Justice Department rolled out the administration’s “zero tolerance” policy to deter a surge of asylum-seeking families at the southern border.

The ACLU and others say the effort to locate the still-separated families has been hindered by incomplete government reports as well as conditions on the ground in the children’s native lands, including gang violence, remote villages and now the coronavirus pandemic.

With the elections less than two weeks away, the updated numbers ignited fresh outrage about one of the Trump administration’s biggest debacles, and one that sharply divided members of his Republican Party. Democrats seized on the new filing to remind voters that the family separations remain unresolved.

“Every day, it seems we uncover new horrors perpetrated by President Trump and his administration,” Joe Biden, Trump’s Democratic opponent in November’s election, said in a tweet.

Lawmakers and advocates for immigrants said Wednesday that the government should do more to ensure the families are reunited.

“I was very shaken by the number,” said Efrén Olivares, who, as director of the racial and economic justice program at the Texas Civil Rights Project, worked with separated families in the Rio Grande Valley. “This was torture.”

The federal judge overseeing the reunifications ordered government officials to hand over records to a group of lawyers and advocates, including Gelernt and his team at the ACLU, who undertook a months-long effort to locate thousands of parents. By now, most of those still in custody when the judge issued the reunification order in June 2018 have been reunited, either in the United States or in their home countries.

But the number of separated families was higher. Lawyers say about 1,500 children had been taken from their parents before the official launch of “zero tolerance” in spring of 2018, while family separations were being carried out during a secretive pilot program in El Paso, Texas. Many of those parents were deported, never given the option of reuniting with their children in the United States.

Trump had campaigned on ending illegal crossings at the southern border, but his plan was thwarted when smugglers began sending busloads of families – often one parent and one child – to seek asylum in the United States. With limited family detention beds, most were released together to await an asylum hearing.

To counter the surge, the Trump administration opted to prosecute parents for the crime of crossing the border illegally, and then separated them from their children.

When parents returned to immigration detention after a brief court hearing, their children were gone.

Officials transferred the minors – some as young as infants – to U.S. Health and Human Services shelters across the United States. A federal judge and government inspectors found that the Trump administration did not have a plan to quickly reunite them.

Of the 1,500 separations, about 500 are not considered to be part of the lawsuit. Gelernt said advocates have contacted the parents of 485 of the children. The DHS says these parents have opted not to reunite with their children, but Gelernt said many parents still hope to come to the United States to be with them.

Of the 545 children whose parents have not yet been found, advocates have managed to reach 183 of the children, and they remain in the United States.

“At some point, we’re going to hit a group of families that becomes very hard to find,” Gelernt said. “It’s not inconceivable that we’ll still be looking for them a year from now.”

When records are insufficient, lawyers must instead rely on a network of human rights lawyers and nonprofit staffers – led by the New York-based group Justice in Motion – who have tried to physically track families on the ground in El Salvador, Guatemala, Honduras and Mexico.

With little more than a misspelled name or an outdated phone number, the attorneys travel to remote, mountainous villages that are sometimes controlled by gangs and where residents often are suspicious of outsiders. The roads to these tiny hamlets are bumpy and ragged, and the prevailing tongue might be the Mayan language of Mam, not Spanish.

These human rights defenders “take the minimal, often inaccurate or out-of-date information provided by the government and do in-person investigations to find these parents,” Nan Schivone, the group’s legal director, said in a statement to The Washington Post, noting that it was already “an arduous and time-consuming process on a good day.”

Then came the coronavirus pandemic.

With strict curfews and other containment measures imposed across much of Central America, Justice in Motion halted its work. The suspicion and trauma common among separated parents – who are no easier to locate these days – has made it difficult to replicate efforts online.

“We had to completely stop because of the pandemic,” one Honduran human rights defender, Dora Melara, told KQED.

For months, as outbreaks of the novel coronavirus spread worldwide, hundreds of parents and children continued to remain apart, now in quarantine.

Some of the pandemic rules have loosened in recent months, but the work remains no less challenging. In Honduras, where people are only able to leave their homes once a week, Melara spends her one free day traveling to visit families, even though she must be back in her own home 14 hours later.

The last thing she and others plan to do is give up.

“When we will find these parents is impossible to know,” Gelernt said, “but we will not stop until we find every last family.”

Some Trump administration officials involved in the “zero tolerance” policy have disavowed the effort. Before stepping down as acting homeland security secretary, Kevin McAleenan said the family separations “went too far.” His predecessor Kirstjen Nielsen told “PBS NewsHour” that she did not regret enforcing the law but was sorry for the prolonged separations.

“What I regret is that that information flow and coordination to quickly reunite the families was clearly not in place,” she said.

Rep. Sylvia Garcia, D-Texas, said Wednesday that the government should do more to ensure that the families have been reunited, noting that it is another example of the administration not caring about the immigrant community.

“This never should have happened in the first place, and it’s up to us now to fix it,” Garcia said.