On Thursday, House Democrats had their first opportunity to lead an inquiry into the Trump administration’s practice of separating children from their parents at the border. As many of them pointed out during the hearing before a subcommittee of the Committee on Energy and Commerce, past investigative attempts were stymied by obstinate witnesses and Congressional Republicans who refused to force those officials to answer precise questions about how the disastrous and unlawful policy came to be implemented in the first place.

Now that the Democrats are in charge of the House, they are able to try to uncover how the practice—which even the administration’s own officials now acknowledge likely caused lifelong psychological trauma to countless children—was allowed to take place.

They did not waste any time in making inroads into these questions. The top Department of Health and Human Services official testifying before the subcommittee on Thursday was Cmdr. Jonathan White. White testified to the Senate judiciary Committee in July, after full-scale family separations were short-circuited by executive order and the courts, that he had warned the administration how badly family separations would go. Democrats on the committee got few additional details at the time, though.

But on Thursday, that changed. White testified about exactly which Trump appointees he warned and that those warnings came in the form of in-person conversations but also multiple emails and memos. Those appointees were HHS officials: Scott Lloyd, Steven Wagner, and Maggie Wynne. (Lloyd and Wynne, for their parts, have well-reported histories of using their positions in HHS as platforms to fight abortion access.)

As White testified, “Separating children from their parents poses significant risk of traumatic psychological injury to the child.” He also said that for many children that trauma would be “lifelong,” even if the government is able to reunite them with their parents. The government has argued in court, though, that it will not be able to reunify many of these families: An internal report estimated that thousands of separated children were placed with sponsors—not reunited with parents—and remain unidentified.

White now says he warned Lloyd, Wagner, and Wynne that separations would be traumatic for these children and probably unlawful. “[I warned] that this would be inconsistent with our legal requirement to act in the best interest of the child and would expose children to an unnecessary risk of harm,” he told the committee.

When he brought this up with his department’s leadership, White says he “received a respectful hearing [and] was advised that there was no policy.”

Still, White says he put his concerns in memos and raised it in meetings starting in February 2017 and running through that spring. He testified that Lloyd and Wynne went so far as to explicitly tell him to not even plan for dealing with an upsurge in separated children. “It was my hope that the reason that we were not planning was that it meant that separation would not occur,” White said. (He added that he believes Lloyd and Wynne also believed separations would not be occurring.)

Those separations did occur, and the hearing illuminated a bit more about when and how they started. Kathryn Larin, of the Government Accountability Office, testified about an investigation her agency conducted, which uncovered that there was actually a precipitous increase in separations beginning in April 2017, soon after White was apparently told there was no such policy. Larin pointed to two points that year leading to the surge: a DOJ memo prioritizing immigration-related offenses and a trial separation “initiative” in the El Paso sector.

According to Larin, this all led to a tenfold increase in separations from the more standard practice of “for cause” separations—such as in cases of suspected child trafficking—under previous administrations. This was all even before Jeff Sessions announced in April 2018 the government’s “zero tolerance” policy, which led to across-the-board prosecutions of parents crossing the border illegally and to additional separations. Zero tolerance has since ended, but Ann Maxwell of the Office of the Inspector General reported that separations are still twice what they were in late 2016 under the Obama administration.

The ACLU is currently involved in court proceedings that are looking to clarify what the current separation policies are and what happened to those potentially thousands of still unidentified separated children.

The next step for Congress, in the meantime, is to continue conducting its own inquiries. Rep. Frank Pallone has already asked for White’s memos warning the Trump administration against child separation, and White promised on Thursday “HHS is going to fully honor your requests.” If that request is not honored, though, the committee has the power and obligation to subpoena those documents. After that, it has the power and obligation to call Wynne, Wagner, and Lloyd to explain what they did with White’s warnings.