Last year, Attorney General Eric Holder Jr. described a federal court trial for the self-professed mastermind of Sept. 11 attacks, Khalid Sheikh Mohammed, as “the defining event of my time as attorney general.” On Monday, Mr. Holder’s dream for demonstrating the power of the American court system crumbled when he announced that the trial would take place not in New York City or anywhere in the United States but before a military commission at the Guantánamo Bay, Cuba, prison camp.

That retreat was a victory for Congressional pandering and an embarrassment for the Obama administration, which failed to stand up to it.