During his presidential campaign, Donald Trump made a pledge to fill the American detention center at Guantánamo Bay with “bad dudes.” He brought up Guantánamo again on Nov. 1, a day after the Uzbek immigrant Sayfullo Saipov was arrested on a charge of killing eight people in a terror attack in New York. Mr. Trump said that authorities should send the suspect to the prison because the American justice system is a “laughingstock.”

But the next day Mr. Trump apparently changed his mind, indicating a preference for trying Mr. Saipov in New York. He said in a tweet that he’d “love” to send him to Guantánamo but “that process takes much longer than going through the federal system.”

Perhaps the president’s shift means he is questioning his earlier commitment to the unlawful and immoral experiment that is Guantánamo. He is correct in saying that the military commissions at Guantánamo Bay are painfully slow at administering justice.

Nearly two years ago, I sat behind a glass wall in the military courtroom in Guantánamo, a mere dozen feet away from the five men accused of planning the Sept. 11 attacks that killed my brother. Greg Rodriguez, my only sibling, was 31 and working as an information technologist at Cantor Fitzgerald in the north tower of the World Trade Center when the planes hit that day.