President Barack Obama has again flip-flopped on national security—and we can all be grateful. Having kept Guantanamo Bay open, resumed military commission trials for terrorists, and expanded the use of drones, the president has now ordered the U.S. military into action without Congress's blessing.

Imagine the uproar if President Bush had unilaterally launched air attacks against Libya's Moammar Gadhafi. But since it's Mr. Obama's finger on the trigger, Democratic leaders in Congress have kept quiet—demonstrating...