President Obama quietly signed an executive order on Monday instituting a system for indefinitely holding terrorist detainees at the U.S. military prison at Guantanamo Bay (Gitmo), Cuba. The administration also announced that terrorist trials by military commission would recommence. This is a win for U.S. security, but the country has paid a heavy price for Mr. Obama’s on-the-job training in counterterrorism. The low-key announcements stand in marked contrast with the bombast with which Mr. Obama approached this issue just a few years ago. During the 2008 presidential campaign, then-Sen. Barack Obama harshly criticized President George W. Bush’s detainee policies. When...