The House Judiciary Committee convened on Tuesday without its star witness. Don McGahn, the former White House counsel and a key witness in the Mueller report, refused to appear after President Trump ordered him not to testify. New York Representative Jerry Nadler, the committee’s Democratic chairman, told the assembled lawmakers and spectators that congressional subpoenas “are not optional.” He also condemned Trump in some of his strongest language yet.

“I believe that each of these incidents, documented in detail in the Mueller report, constitutes a crime,” he told the committee. “But for the Department of Justice’s policy of refusing to indict a sitting president, I believe he would have been charged with these crimes.” The hearing, which largely focused on an empty chair, still received wall-to-wall coverage from news networks and political journalists.

The president’s misdeeds surrounding the Russia investigation can’t be ignored. A tragedy of the Trump era, however, is that it’s hard to know which episodes of wrongdoing to prioritize. Foremost among them should be the Trump administration’s handling of the desperate, vulnerable people crossing the southern border. The inhumane treatment of these migrants is not an impeachable crime, but it may prove to be the deepest scar his presidency leaves on the nation.

The most visceral evidence is the death of young migrants in U.S. custody. On Monday, Carlos Gregorio Hernandez Vasquez became the fifth Guatemalan minor since December to die after being taken into U.S. custody at the border. Customs and Border Protection officials did not announce the 16-year-old’s cause of death, though a U.S. nurse reportedly diagnosed him with the flu over the weekend. Other migrant children who have died in U.S. custody recently also reportedly had infections or flu-like illnesses, raising questions about whether the Department of Homeland Security is doing enough to ensure the health of detained minors.

As for the adults in its custody, the department has held an untold number of them in cruel and unusual conditions. The International Consortium of Investigative Journalists obtained more than 8,400 incident reports from Immigration and Customs Enforcement, an agency within DHS, about migrants put in solitary confinement in recent years. Officials placed many of those migrants in isolation for months and weeks at a time, even though the United Nations recommends no more than 15 days. The rationales ranged from hunger strikes and disciplinary measures to consensual kissing and having a physical disability. And ICIJ found that nearly a third of those placed in solitary had a mental illness, even though the U.N. says the mentally ill should never be subjected to solitary.