President Barack Obama swore as far back as 2008 he’d close the U.S.-run prison for terror suspects at Guantánamo Bay. Five and a half years later, he finally took a real risk to get that process moving. The president defied Congress over the weekend, ignoring a 30-day notice rule required by law to greenlight the transfer to Qatar of five alleged members of the Taliban held at Guantánamo in exchange for the release of Army Sgt. Bowe Bergdahl in Afghanistan. It’s Obama’s most assertive move to shrink Guantánamo’s population since U.S. embassy bombings suspect Ahmed Ghailani was flown from the...